Same as always, the hope that as many slot machines as possible can be preserved and emulated before they vanish forever. Yes, from crappy old 3-reel mechanical games right through to modern PC-based hardware (MAME doesn't actually emulate any "American style" 3-reel slots to my knowledge, for example, one solitary S+ game is preserved in MAME but emulation is next to nonexistent, it isn't even close to the likes of fruit machines).