The two replies cover why multisig helps. The part that decides whether it's worth it for you is what you have to back up, because it's different from singlesig.
With a 2-of-3, two seeds alone are not always enough to recover. The wallet is defined by all three public keys plus the script (the "output descriptor", BIP 380). Two seeds give you two of the xpubs; the third xpub lives only in the descriptor/config file. Lose that file and one seed, and you can be stuck even though you still hold two seeds. So the usual practice is to store a copy of the descriptor next to every seed backup (it's public info, it can't spend anything, but it does reveal your balance).
https://github.com/bitcoin/bips/blob/master/bip-0380.mediawiki
Rough way to decide:
- Singlesig fails if the one seed is found OR lost. If your realistic risk is someone finding the backup, a BIP39 passphrase is a smaller step: the seed alone no longer spends, but now forgetting the passphrase loses everything.
https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki
- Multisig 2-of-3 survives one seed being stolen or lost, and lets you split keys across places or people (useful for inheritance). The cost is more devices, more backups (including descriptors), and a recovery you should actually rehearse on a small amount first.
If you can't see yourself testing a recovery with two devices and the descriptor, a well-done singlesig plus passphrase is often safer in practice than a multisig you've never restored.
