When you receive a transaction, the amount is split into thousands, hundreds, tens, ones, etc. So if you are sent 1234 TRTL, this is stored as 1000, 200, 30, 40
in your wallet.
When you want to send a transaction, regardless of how much you are sending, you have to use these stored amounts. If we wanted to send 10 TRTL, and you only have a 1000 TRTL input, you have to use this.