I can do that without Tailscale though by just using the WireGuard app. What is Tailscale adding to this?
Tailscale also provides a "magic DNS" service which lets you resolve your Tailscale device names without setting up unbound etc, and which can relay other requests through to your pi-hole or unbound or whatever, which can then listen only on the tailscale IP address, so no need to run an open resolver or deal with source IP filtering.
e: also, you can share devices between tailscale users without generating, managing, distributing wireguard secrets. You send your pal/partner/kid a link and they can access your fileserver or raspberry pi webserver or pihole server for themselves wherever they are.