If you are talking a professional type coating, it does not "chip off" and you see little pieces of it on the ground, etc...
If you want to take the time or the Client is paying for it, it is Always a great idea to take the wheels off, clean them perfectly, wipe them down, and coat the entire wheel, inner wheel and the back lip of it...
I did mine years ago and love having no brake dust problems and the wheels always look clean even when they dont get washed for weeks, etc...
They are so easy to wash since I did that, it's not even a chore to do like it used to be before I coated them...
By the same token, it makes perfect sense to coat everything outside that is able to be coated, making the washing and maintenance so much easier..
Now, if you like to go do things to your paint all the time, then coating is not going to work for your because it does not require a lot of maintenance - well, at least the really good ones do not require a lot of maintenance...
Good luck with your research !
Dan F