Originally proposed here
The idea is that instead of tracking balances and allowing deposit/withdraw on individual contracts, we create a NativeVault (I guess a similar mechanism for ERC20s) that holds all funds for proposers, provers and other actors of the rollup(not to be confused with user balances, that is a very different conversation).
This is only beneficial if we have more than one contract where the same actor(s) need to deposit/withdraw some since it isolates the logic and make it more capital efficient. At the time of writing this, the only contract with these requirements is the ProverManager.