It just makes sshing between the machines by name very easy. You can do the same thing by assigning permanent IPs to all machines in the mesh and then updating all your host files across all the machines in the mesh. Life is too short for that.
It takes a few seconds to connect each new machine. It took me way more just to find out how I should configure Cisco's VPN client, and I do not ever want to even think about OpenVPN again.
I've also maintained a WireGuard mesh where I distributed keys and set up /etc/hosts via ansible: add a host to the inventory file, run the playbook - simple.
Yet Tailscale is even simpler than that. And (for my purposes at least) it's free.