If you are ever going to install heated grips, it makes sense to do them in advance of installing the barkbusters. Otherwise, you will have a duplication (triplication ? , really) of labor involved in mounting them, taking them off, then mounting them again.
It's not a big deal I guess, but I hate doing unnecessary work.
As far as "needing" heated grips, there's dudes in Florida that rock heated grips. They are nice in any climate for warding off chilly night air, damp morning air, etc. I think every time I've ever ridden to Naples to see my parents I've used the grips on different stages of the trip.