Zk rollups are about as fast as visa network - and recursive zk snarks can scale further if needed. The benefit is that they inherit the security of the main network - users can withdraw tokens from them trustlessly, and at no point can the rollup owner steal user funds or block them from withdrawal.
For financial services like lending and swaps this is great and avoids some of the CeFi and CEX problems we are seeing. For other apps like art sales, public groups, and ENS domain name aliases, it allows ownership of assets to be held non custodially rather than a single company’s servers and records.