It provides a consistent IP address (in the CGNAT range) that the end-device is always reachable at. On top of that you can use MagicDNS or regular DNS records to refer to it.
That IP is usable regardless of how that device and your device actually reach the internet. Further, no one device acts as a “server” and needs a stable public IP thanks to NAT traversal and the DERP fallback path. Keys are handled automatically with an option to not trust Tailscale infra in doing that (Tailscale lock) and I just need to auth devices with my Google Workspace/Gsuite SSO.
Plain vanilla wireguard involves a bunch more faffing about with wg, wg0 and keys. With Tailscale, you (can just) install the software on each computer and then log in. There are also more advanced things you can do with Tailscale, but I chose Tailscale because of wanting to not have to deal with the setup like Wireguard (or OpenVPN) have.
