I often hold down two strings with one fingertip. It doesn't hinder playing at all; in fact, it frees up a finger for adding twiddly bits here and there.
I never really got the hang of using three fingers to hold down the open A major chord, but why use three when you can do it with 2 on even 1?
I wish this forum had a "block user" feature. Possibly I'm not the only one......