Many reasons:

We bought a couple pigs together and offer them local to friends and family, proceeds go back into the multisig between us.

I set an organization I support up with a wallet, I hold 1 key they have the other two. I can pull address to send sats monthly for support, but can spends funds. I’m also there as a backup if a key gets lost.

Could also put sats in for a bet or pooling your money to do something together in the future.

Cheers 🤙🏽