There is a skinny stance craze going on now? Sweet I'm back in style
I've been riding 20.5"-21" stances as that the widest I can go without serious ankle/knee/hip pain (tried mutiple canted bindings). I'm guessing it is because I have narrow hips (30" waist) and short legs (30" inseam even though I'm 5'9") and because my ankles are messed up from too many ankle sprains... .
Narrow stances are noticeably little less stable, but not huge (I still have landed 65+ ft jumps with my skinny 20.5" stance).
It is a bit harder to press a board though (hence why I was trying to go with 22" stance, but my joint won't let me do that for long).
There is some benefit in free-riding/boardercross/racing as you can turn power the board more. When you see the guys in boardcross, they have slightly narrowed, forward angle stances... but you can see they looking a little less stable, but they are still hitting some decently large jumps.
I've not heard it being done by park rats though... last I checked they were still doing ridiculously wide 24-25" stances which is fan for a giant like Andreas Wiig, less so if you are like a 5'6" kid.