There's a small transaction fee for very large transactions. The payment processor that generates the code that contains the transaction gets the fee.
If the same money gets sent again, it won't incur the fee again. If all you have is generated Dollars in your wallet, if you send them all in one huge transaction, it has to bundle hundreds of 50 Dollar bills together. After that it's just one line to send the combined unit.
Does the sending client send more Dollars to account for the fee (so the recipient gets what he's expecting)? Why couldn't someone just send 1000 small transactions to bypass fees?