Is there an advantage in leaving my Play:5 (gen2) connected in ethernet vs wifi?

If you've always had the Play 5 connected to the router via Ethernet then you may/probably have never entered your Wi-Fi details so it wouldn't work if you un-plugged the cable. But as you only have 1 Sonos unit it won't make difference. I'd just leave it as it is

Thanks for your reply Stuart.
We just moved to a new place where it is now next to the router but it knows our wifi and everything...
A cable more or less in the unit doesn't matter but I was really just curious :)
Cheers

Wired is always more stable than wireless, but the trade off is less freedom of movement. That goes for any device, not only Sonos. If you want to try wireless just remember that having the speaker too close to the router can cause interference.

I am going to respectively disagree with some of the other posters. I have found that Sonos does not do particularly well when multiple units are on the same LAN and hardwired while others use Wifi. I had all my Sonos devices hard wired and was experiencing quite a few dropouts. I ultimately sent the diagnostic log into Sonos and some kind of a network loop apparently existed where my Play:5 unit was trying to connect both on the cat5 LAN as well as the Wi-Fi network. Ultimately we removed the cat5 connection and reset the units Wi-Fi so that it went back to the Sonos Mesh. This cleared up all the problems. My advice would be, if it is working, leave it alone, if it starts to act up, eliminate the cat5 connection, reset the wifi for the controller, and go back to the standard Sonos Mesh. I am running a full blow Meraki network and this is my first real Sonos issue in over 5 years so you may never have a hiccup like I did.

I am going to respectively disagree with some of the other posters. I have found that Sonos does not do particularly well when multiple units are on the same LAN and hardwired while others use Wifi. I had all my Sonos devices hard wired and was experiencing quite a few dropouts. I ultimately sent the diagnostic log into Sonos and some kind of a network loop apparently existed where my Play:5 unit was trying to connect both on the cat5 LAN as well as the Wi-Fi network. Ultimately we removed the cat5 connection and reset the units Wi-Fi so that it went back to the Sonos Mesh. This cleared up all the problems. My advice would be, if it is working, leave it alone, if it starts to act up, eliminate the cat5 connection, reset the wifi for the controller, and go back to the standard Sonos Mesh. I am running a full blow Meraki network and this is my first real Sonos issue in over 5 years so you may never have a hiccup like I did.

You were experiencing a network loop due to STP problems. This has no bearing on the OP because they were speaking of a single wired unit, and STP problems only arise with more than one wired unit. Even so, STP problems are usually fixable by configuring your router and/or switches to properly support STP. See this link for details:

https://en.community.sonos.com/troubleshooting-228999/sonos-and-the-spanning-tree-protocol-16973

In fairness, jgatie is correct in everything he says, and the issue is/was related to an STP problem. Unfortunately, no configuration of the port stopped the issue from occurring.