Coin Control

Coin control is a wallet feature that lets you choose which of your unspent outputs a transaction will spend, instead of leaving the choice to the wallet's automatic selection. It applies only on UTXO chains, where a balance is a set of separate outputs rather than a single number. There are two reasons to use it. Fees: a transaction grows in size, and therefore in cost, with every input it includes, so spending one large output is cheaper than sweeping several small ones. Privacy: combining two outputs in one transaction is public evidence that the same wallet controls both, which is exactly what an observer needs in order to link addresses that were otherwise unconnected. It is also the standard response to unsolicited dust, because marking a suspicious output as unspendable keeps it out of every future selection. Whether the feature exists at all, and what a wallet calls it, differs by application.