The Pay-per-Share (PPS) mining pool reward system, if offering an instant flat payout for each share that is solved by the miner participating in the current block solving.
The payout mentioned above is usually offered from the pool's existing balance and can, therefore, be withdrawn immediately, without waiting for block confirmations or solutions to occur.
The possibility of cheating the miners by the pool operator and by timing attacks is thus theoretically eliminated, and is usually the preferred method for miners.
PPS provides the least possible variance for miners while transferring all risk to the pool operator. The resulting possibility of loss for the server is offset by setting a payout lower than the full expected value.