[Zababa]

> As for asymmetric titles like Mario Galaxy where the second player is not essential, it's pretty hard to make the gameplay satisfying for the secondary player while not impeding the first player or making it feel essential to the gameplay. The "little brother" mode costs a lot with little perceived benefit for the developers.

I'm not sure how frequent this is, but when I was little we (me and my brothers) had limited time to play, so we would play our time and watch each others, sometimes completing long missions in Ground Control by playing one after the other. When you look at it this way, having something to do instead of just looking at the screen (which was already plenty of fun) is huge.