To know if someone is really that account you should check the npub, but that is really long and hard to read.

NIP-05 Verified simplifies that; NIP-05 makes the npub more 'readable'. You can quickly scan if it is really that person. Because the verification is linked to that npub only others cant use it.

Not the most secure way, you can fake a domain (like using the l for I) and need to trust the provider they cant get injected by attackers.

Mostly it's just great fun and a cool way to identify yourself with others or show your support! (Some providers ask for sats and use that sats to fund devs, love that!)