I feel like the best apps for me are stuff like Drafts. Anything that lets me voice capture an idea reliably while doing something else, like driving.
I realize that Siri in theory can do this stuff on the phone, but the on-device stuff via the Watch, triggered by a corner tap, is more reliable for dictation.
I think that if you need to be convinced then you should probably not get one, unless the expense is of no significance to you.
For me the absolutely killer feature is that it unlocks my Macs. My Macs are locked every single time that I leave the room, or even if I’m going to be on the other side of the room for a while, so having something that unlocks them automatically is wonderful.
Apart from that, ApplePay, notifications, and MFA acknowledgement are all great benefits too. That last one will likely be at or near the top of the list once my workplace gets more into MFA. I’m a runner, so having weather information on my wrist and fitness tracking are nice to have too.
None of that stuff, apart from unlocking (and eventually MFA acknowledgement), are compelling reasons (for me) to get a Watch; they’re just nice to have.