Best answer by MikeV
1. Give you WiFi you have control over, so you can adjust settings as needed.
2. Give you an Ethernet port, in the event that it should be necessary (settings in the router usually allow the port to be switched between WAN and LAN functions; LAN would be recommended if you're using WiFi as your WAN connection).
3. Give you extra security... keeping your devices on a separate network from everyone else's!