I didn't use them for years - until one day when I really sat and messed with them, and realized - they do wonders for my kit.
I use 2 on my tom, both on the outside edge, one at 12:00 , the other at 6:00. I use 1 on my floor tom, at 6:00. (Closest to me). And I use one on the snare - outside edge, 6:00. (again, closest to me)
I think using one on the snare must be similar to how Ringo Starr used to keep his pack of smokes sitting there while recording.
I just like the deader, dry drum sounds, personally.