Tailscale is an abstraction layer built on top of Wireguard. It handles things like assigning IP addresses, sharing public kegs, and building a mesh network without you having to do any manual work. People like easy solutions, which is why it's popular.

To manually build a mesh with Wireguard, every node needs to have every other node listed as a peer in their config. I've done this manually before, or you could automate it (eg using Ansible or a tool specifically for Wireguard meshes). With Tailscale, you just log in using one of their client apps, and everything just works automatically.

I don't think there's any significant downsides. I suppose you are dependent on their infrastructure and uptime. If they ever go down, or for any reason stop offering their services, then you're out of luck. But yeah that's not significant.

The reason I want to do this is it gives me more control over the setup in case I ever wanted to customize it or the wireguard config, and also teaches me more in general, which will enable me to better debug.