It's often just a matter of "what you want to do".
Depending on the smoothness and epicness of your animation, you might want to cut every little pieces or almost none.
Basically, I advise to keep as few different parts as possible, if you have to do tons of animations with it. (and vice-versa)
If really the animation looks strange, you can still slice new pieces anyway.
For example I often start with foot+calf being only one big limb, but if it looks odd, I keep the calf animation, but slice out the foot from the symbol, into a new one I animate additionnally.
That said, separating eyebrows, mouths, eyes and some hair pieces always come in handy, to animate separately inside a global "head" symbol (or outside, on animation root, if your animation will have a very static head through all of it)
Nesting can be really powerful indeed, but personnally I never found a way to nest boobs or arms into torso part, because... you really just need them to do far too complex moves to nest them, alas.
For limbs connexion, I suggest using the fact limbs are gonna overlay each other to extend some limbs.
For example knees and elbows can often be "hidden" in overlayed parts of upper/lower arms/legs, for them to look as good when straight or bending.
Use the fact the limbs will cover each other to hide additionnal chunks of body, don't just "2D cut" your stuff.
(anyway, usually obvious in the first minutes of trying, lol)
For the 3/4 view, you are quickly very limited, on "multiple characters interactions" (who said "sex" ? Well, I did ^^).
With 2 characters in 3/4 view, it will quickly look odd, aside from spooning poses.
But yeah, it add a powerful visual value, when you can place it
Again, depends on what you plan to do with it!
Always a compromise between the time you will spent animate it and the smoothness of the result.
As example, my slice from KoPC. Which isn't complete and looks crappy as hell, I know, but this price paid allowed me to offered dozens of customs and alternate skins for every single parts, as well as to do a hundred different sex poses, from 1 character to 5 charactes involved.
Basically, I just confirm what already been said, lol, but it just shows there's a logical reason we all end up with that kind of slicing process.