This! WiFi is needed for handoff features. So, make ethernet your top priority and let WiFi do the handoff stuff.
BTW, AirPrint\Play just needs to be on the same subnet, not necessarily on WiFi. For instance, if a Mac and ATV are both hardwired, you can Airplay to the ATV over the LAN. This is because air* uses bonjour to discover devices, and bonjour is not routable, it uses ARP-like layer 2 discovery. Some routers may only support bonjour when UPNP is enabled, so check with your router documentation. But most routers keep LAN and WiFi on the same subnet.
So, unless you connect to guest WiFi, which is often set aside on a separate LAN segment, wired and wireless devices can air* without issues.