Because of all the games available now, it can actually take a little bit to work through them with any recent group of Streetpasses. Anyway I was short for time, so I did the Garden, Mansion, and Battle games and decided to let the Squad game slide this time (one ally wasn't worth it, I'd only be wasting 10 minutes to get my ass kicked.)
But, closing the plaza and coming back later...that Mii was still ready to help me out in that game! Meaning I can save up these dudes and unleash them all together to enable a better shot at finishing these harder rounds.
I'm assuming this applies to most if not all of the other titles too....could be useful.