It's great if you use it at a place where you're a regular, and have told Square to check in automatically based on your location.

Order drink, chat with server while they make it, they know by now you're probably paying with Square. Done.

vs.

Order drink, chat with server while they make it, dig in purse for wallet, hope it's not one of those days where you accidentally left your wallet back at home while switching bags. (Yes this really happens to me sometimes.)

If you have, say, a coffee shop you regularly go work at, and they use Square, Wallet is totally awesome.