Good clip. So back to the original Q, control is basically the practice of labeling and using your UTXOs in an intentional manner. As odell says here, not all wallets even show your utxos. If you have only used such wallets, this is probably confusing

Bluewallet for mobile and sparrow for desktop are intuitive and allow you to “do coin control”.

Also worth noting, this is a local/client-side feature!! If you have the same bitcoin wallet in both of those programs, and label one in sparrow, that will NOT show up in the same wallet on bluewallet