For most of the mesh units with the option simply means the devices form the mesh using the ethernet instead of a wifi connection between each unit eating into available bandwidth.
Then surely it's not a mesh any more, they're just multiple overlapping access points on Ethernet?
I have to sort out the networking at my parents house soon. Their VM service comes in on first floor so that's where the hub is but, as it's a 100+ year old house with thick walls, the Wifi signal downstairs is shocking.
We've tried extenders and powerline but been disappointed with both.
I've thought about mesh systems but frankly don't trust them and can't bring myself to drop hundreds on a system that may not even work properly.
My intention is to run Ethernet downstairs, possibly outside the house for simplicity, then just use an additional access point downstairs. Cheaper, more reliable and I have 'native' (as opposed to via the Wifi mesh) Ethernet downstairs too.