@shroy100 - Sorry you felt like people were being condescending. A lot of people prefer to read through info and decide what bits to pick out for their riding style and which to ignore, all on their own w/o being told specific things to do and why. You seem to prefer specific examples and the reasoning behind them. That's fine, but to flip the coin, it's kind of like saying you can't be bothered to sort it out on your own when given resources to view. You don't want to do the "homework", just want the answers to the test.
LD riding is a progression of experiences. You do a ride, things bother you or impact your comfort, so as
@kerrizor wrote about, you take a look at what those issues were and start trying to find ways to eliminate or improve them. Then after the next ride, you repeat that process. Eventually you have YOUR process dialed in to what works best for you and fits your needs. It's not the same for everyone, but there are obvious similarities you notice if you're around this crowd for any length of time. And that's not limited to what you wear, but to how the bike fits you, what you drink and eat too.
It's hot so you wear less is common for riders that don't do long hours in the saddle. Hey, it works great for a day ride. But exposure over time means your body can't handle the heat/wind as well and it tries to cool you and prevent your skin from drying out by sweating more fluid out than you can recover during the ride. The more exposed skin, the more fluid you lose. It seems counter intuitive to wear more clothes when it's hot, but it's a tactic that's used all over the world and has been for centuries. The Bedouins in the deserts wear long flowing robes for a reason, to keep the skin covered and allow air to flow around them. That works at walking speeds, but at motorcycle speeds you need tighter fitting gear to avoid it flapping all over.
The basic idea of keeping the sun off your skin is the same.
Wearing your jacket from the start means you don't ever get 'cooked' to begin with and you lose less fluids. Yeah, you're going to sweat still, but the air isn't blowing over you and evaporating it instantly, so you will notice it more. That leads us to a base layer that doesn't allow the sweat to just sit on your skin and irritate it. LDComfort uses a material that holds moisture, but keeps it off your skin to prevent irritation. Another benefit to that is that any airflow that does pass over that moist fabric works like a cooling system for your skin. In any temps over body temp, (~96F), you're fighting a losing battle of trying to keep cool by just exposing your body to the air. And more air flow, like mesh gear, just means more fluid losses at a faster rate. At lower than 96F temps, evaporative cooling still works very well.
I will wet down my base layer of
LDComfort shirt when it's hot and zip up my jacket, just leaving the collar open a little and my left sleeve cuff. When I'm moving, if I feel hot, I'll stick that left arm out in the wind or angle my wrist on the bars a little more so wind blows into the sleeve. It inflates the jacket a little and blows it out my collar, cooling me off like opening the fridge door. If I ride with everything open and wet base layer it's great... but only lasts a short time. If I do the single cuff and collar trick, it might keep me comfortable for 2 hours or more before I need to wet down again. Sometimes I leave both cuffs open a bit and alternate which one I stick out into the airflow. The more you open up, the faster the water evaporates. Sweat will have this same effect, but forcing your body to produce the moisture for cooling just means it takes less time to get dehydrated. Once you're there, it's too late to recover during the ride, you will continue to be dehydrated for the rest of the ride, no matter how much fluid you drink. The body needs TIME to recover then, as well as fluids.
As I said and others have commented on, noise is a stress factor. The more stress your body is under, the more work it has to do to counter that stress. Vibration, noise, heat, cold, poor circulation, discomfort, bright light, etc are all stress factors for the body. Basically, your bodies comfort
IS a safety issue. The more comfortable you are, the easier it is for you to ride well, notice everything around you, think more clearly and focus better.
Dehydration makes us stupid. Our brain functions actually slow down as we get dehydrated. We start making poor decisions or missing steps, (like leaving the gas cap on the pump). There is a tipping point with dehydration where you can't take in enough fluids to offset being dehydrated. It then takes a lot more time to get back to being properly hydrated. Like a couple days before you're back to normal. That's why we talk about a lot of small sips over time being better than pounding a bottle at a gas stop. If you think about taking a drink, that's your brain telling you you are getting dehydrated. When I think about taking a drink on the bike, I take a drink. There are a lot of different ways to do that, but that's a whole new topic and has many, many solutions for different people.
You wear sunglasses because it's uncomfortable to squint into the sunlight, sudden bright reflections off car glass, water, etc. You still see everything, it's just toning the light down a notch. Less stress to the eyes/body.
Ear plugs are like that, toning down the noise that gets through to your ears a notch. You still hear everything, its just not quite so big an impact. Less stress to the body.
Half shell helmet Vs a modular or full face. At highway speeds the air is usually pushing the half shell helmet up off your head unless you're riding behind a big ass windshield. That's a stress factor for the body too. And your face is more exposed to wind/heat as well. Your eyes are getting more airflow usually too, depending on your shades or goggles, which can cause them to dry out, so your body produces more tears to offset that as a response. More stress to the body. A modular worn in the closed position or a full face helmet means that you're not getting as much air to your face/eyes and not getting potential bugs/tiny debris when trucks go by and what ever is in the wind hitting you. Ever follow a truck loaded with hay? Then you get the idea.
I prefer a modular so I can flip it up at stops or to talk to another person when needed, as well as it being easier to take a drink while riding or even eat while riding, (common among LD riders).
But, the bottom line on helmets is that it has to FIT and be comfortable. A new helmet is always on the tight side, it has to be to work and protect you if you crash. But they come in different shapes because our heads come in different shapes. Maybe you're a round head guy. Maybe you're an oval head guy. I have an oval head shape, so I look for helmets with oval or semi oval shapes and find one that feels good. If you can wear it around the shop for 20 minutes w/o getting a red spot on your forehead, that's often going to be a winner if you're an oval head shape. If you're a round head shape, it's usually the ears that don't fit and get to bothering you first. Yeah, it's a pain to go thru that process, but it beats spending the coin on a nice helmet only to discover on the first ride that it's a constant discomfort that you're always thinking about. You can do the same with mail order, you just have to make sure what the return policy is and be ok with that, then wear it around the house w/o taking the labels off until you know you're good with it's shape.
I cut my teeth on a '40 Knucklehead chopper back in the '80's. I rode for a decade w/o helmets, just goggles, and a snoopy when it was cold. When I bought my first full face helmet I had a hard time getting used to it. It felt like my head was in a bucket. I mostly wore a half shell then because of helmet laws in various states. Then I got into autocrossing with a sports car. You have to wear a full face helmet for that. Even inside a closed car. Doing that, having to focus on the cone course and drive hard, got me used to full face helmets faster. After that, wearing the full face helmet on the bike was no big deal. I had gotten used to it and still being focused on driving, so focusing on riding was easy. It just took some time with my head in the helmet to get to that point.
All this group is saying is there are ways to make long distance rides less stressful on your body and more enjoyable to you. You'll be less tired during and after the ride and be better able to deal with any conditions you encounter during the ride. Try this stuff or don't, it's always up to you.