I need a really dumbed down explanation of all this, because I don't quite get it. Is it basically saying that you are fragmenting your wallet address with each transaction or am I just being silly now?
Actually, yes, in most cases.
It starts with an explanation of how all coins are created and sent.
On the blockchain, coins begin life as a 'block'. This is created in mining, and in say the case of Bitcoin, it is 25 coins. This is created in the Miners address.
When a transaction is made, a portion of coins sent from that single address (in say, a wallet) can only be transacted as the whole block, and 'change' is sent to another address.
Example: 25 coins (block) in a wallet, sending of 10 coins to another wallet : 25 coins are sent to the receiving address , and 15 coins 'change' are sent back. This can be to a new address, or the same (sending) address, depending on the wallet function..
This process continues with every transaction, thus blocks of coins are split down into smaller 'packets' of data. Recombining can also occur when sending a larger transaction. The default wallet function varies in each coin, but often involves creating a new address for 'change', and existing addresses can be reused, or not according to preference.
Thus the coins in a wallet (even within the same addresses) exist in smaller 'packets' of data. It is the quantity of
data in those packets that dictate the 'size' of any transaction. Where a large number of smaller packets are required to be sent the transaction is 'large'.
'Coin control' is a wallet function in which you can see details of all 'packets' of coins, and select discrete packets for sending. These can be sent back to the same address as well, thus recombining the fragments as needed.
