......... Since it hurts nothing to just leave it on, ..........
Head weight, for one. It's easy to overload a tripod/head combo when you get a big camera, long lens, and throw a 4-way focus rail into the recipe.
It's never happened to me in all the years I've been shooting big cameras with grips and long lenses on tripods with focusing rails and/or other attached gear (like lights, triggers, transmitters, etc), so I don't think I'll start worrying about it now.
Apparently, it's not as easy to overload the head as you seem to think, unless of course you're working with inferior gear that can't handle the loads you work with, which is entirely up to you. I prefer not to do that though.
.........Please explain the logic of taking it off and putting it on and taking it off and putting it on and taking it off and...
It's the same logic as changing lenses, filters, hoods, flashes, flash modifiers, batteries..... You get the idea.
No, actually I don't get the idea, nor do I see any actual logic in it.
I
HAVE to change those other things you listed in order to effectively deal with different subjects and circumstances in order to get the
LOOK I want for each photo. I don't
HAVE to take my grip off and put it back on and take it off and put it back on to get the
LOOK I want for each photo.
In fact, I see it as a waste of time and energy to take it off and put it on and take it off and put it on and take it off and put it on and take it off and put it on, over and over and over, shoot after shoot after shoot after shoot, all day long, day after day after day.
Why don't you try again? Reach even deeper into those dark recesses and see if you can find a
real point to taking it off and putting it on over and over and over again.