It depends.

It'd be handy for me: The fastest WAN pipe I can get is less than a gigabit while my LAN is still gigabit. I can't be the only person with this situation, wherein: If anything, then the 2.5-gig port is overkill.

I don't have any direct interest in the wifi radio that the box includes (I already have Mikrotik APs that I like just fine), except to configure it as a failover station-mode interface to use with a phone hotspot when the DOCSIS connection is on the fritz.

...which doesn't happen often at all, but it's annoying when it does happen. It's nice to be able to work around problems like that with OpenWRT.