However, "current monitor" actually means your primary monitor regardless of the placement of the skin, overlapping with the functionality of #PSCREENAREAX#, etc., unless the user goes and digs up this obscure setting in Manage, "Auto-select based on window position". Moreover, it has to be set on a per-skin basis. There is no way for the skin author to control this other than including a layout. I only learned this today from a user complaint after testing on a friend's computer as all my monitors are the same resolution.Screen area position and size of the current monitor.
I can't think of any reason how AutoSelectScreen can harm users by being on by default, or break backwards compatibility, but it definitely hurts usability by being off. Rather, it seems more likely that a only few users may want to turn it off for specific skins.