I use the same key, but technically the difference is that you store your key in a bunker (I use nsec.app, a bunker running in your browser) and the website communicates with that bunker, instead of you having to insert your nsec to some website. If you use the nsec, Noogle stores private keys only locally, but in general it's a bad practice to insert your keys on websites, so a signer is always to prefer. You can also use a nip46 bunker address, a browser extension etc. also see the video in the replies about the signer.