In Binding of Isaac: Rebirth, luck has been made a visible stat. (It was present in the original game, but not shown on the stat screen, unless I just totally missed it). However, even with 2 or 3 points of luck, I still find myself gulping down random pills which have a negative effect such as stat downs. (This could of course be confirmation bias). I've also not noticed much other impact of being lucky.
So if being lucky doesn't seem to impact things like pills and the stuff I get from beggars etc., what's it good for? There are items which specifically increase your luck such as the Lucky Foot, so it must do something.