I see some bowls at the home centers that wobble like a rocking chair. I won't install them.
If a bowl needs shimming, the make sure it's is the back that is shimmed, not the front. If you rock the bowl back and forth, it will break the seal, and you will be redoing the tile when the floor is ruined.
Use a water base caulk; grouting the bowl to the tile may mean breaking it out with a hammer when there is a problem.
Don't' laugh, we do it all the time. Just remember to wear eye protection and watch the sharp slivers of broken glass like porcelain.