I’m sure there were other uses.

Choking your little brother when he beats you at Pokemon?

(I have no idea if that’s how it worked, I didn’t have Pokemon for my Gameboy.)

TETRIS.

Some newer games only needed one game to play with 4 players.

I believe Mario Kart was one of them, then some other game with a motorcycle looked from the side.

I played those on the Gameboy Advance with the nieces and nephews during family parties.

It was the only two-player game everyone definitely had.

Yeah PVP Street Fighter!