Well for instance protein doesn't matter for anything but an elite trainer, whether it is consumed in one portion or in many, or when throughout the day.

Carbohydrates do have a localized effect but the amount is definitely blown up for selling health fads.

As for me, I'm on some medications you take all at once and some taken throughout the day because the body processes them differently. Someone on insulin and someone with ADHD take their medicine quite differently, as an easy example.

I genuinely don't know with caffeine and am curious.

Because if you took less at a time your body will have already processed some of the previous dose before you take the next does. You shouldn't eat 5 pounds of black liquorice in one sitting because it's toxic in that amount, but you can safely have that amount spread out over time.

Imagine taking 6 ibuprofen all at once instead of taking 1 or 2 every few hours. That would absolutely not be a good idea.

Everything on earth that can be consumed has a dosage that is too high to safely take all at once, even water. You're not just pouring this stuff into an isolated beaker.