I struggled with a use case at first as an individual user, but now I'm using it in a few different places.

I have a Synology on my home network which I use for Time Machine backups among other things. My Mac has a Tailscale client and I can backup to my Synology from anywhere.

I have a number of random servers I keep for hobby stuff, a mix of hosted bare metal, VMs and VPS. None of them have SSH open to the internet. My access is all over Tailscale. It was super easy to setup, and now I never have to touch it. Occasionally I'll see that the Tailscale daemon was updated on some host.

If I were starting a company today, as soon as I had any resources that needed any kind of remote access for the team, I'd use Tailscale to provide that access.