How much hate for Flappy Bird in this topic... I don't like it either, but I'm not a fan of mobile gaming in general so I would think that almost any mobile game is useless! But since I'm not a fan, my opinion wouldn't be actually honest...
No, for me there are two kind of useless games: the joke games, like the Steam Summer Sale Simulator (yes it's a thing) or those weird simulator like Dinner Date where you play as a guy waiting for his girlfriend (spoiler: she doesn't come), or The Graveyard where you play as an old lady that walk in a cemetery - seriously, what?!
But another useless kind of game is simply a game you don't enjoy. Why would you play such a game? You play to have fun, and if you don't... well, no much use for that game!