Not much...it shaved off just a little weight (30F down bag to 30F down quilt). It's smaller to pack and now I don't worry about the zipper pull snagging or potentially poking a hole in my hammock.
I have had the concern about "what If I go to ground??". So far it hasn't happened and I carry a torso length pad anyway. Worst case scenario I go to ground on my foam pad and still cover up with my quilt. No real change from having my sleeping bag.