Found a great description:

'What can we do with a SNARKs-enabled Ethereum? Certain contract variables can be effectively made private. Instead of storing the secret information on-chain, it can be stored with users, who prove they’re behaving by the rules of the contract using SNARKs. Each of these uses require their own trusted setup, but once a circuit exists, it can be easily cloned. Imagine an ERC20-like token that doesn’t publish individual holders’ balances, while still maintaining a public and predictable token supply, or a lending platform that keeps the terms of a loan private.'

https://decentralize.today/zero-knowledge-proofs-zcash-and-e...