I keep my games off when I'm not playing/not around them at home and in the shop. At the office I'll keep them on all day but turn them off before heading home. Everything I have is 80s vintage at newest and while they're pretty reliable that's old enough that things will fail just on account of the passage of time, and I'd rather that not happen when no one is around to catch it. If a coil locks on or the GI connector cooks while someone is around to smell it it's a simple repair, if it happens overnight it has potential to be something much much worse. I'd worry less with newer machines but I'd still turn them off just to keep the hours low on components... Everything has a time to failure.