Interesting. For me, I've had one time I used a club without flying. I was picking up my nieces in San Diego, and they were flying Jet Blue, which is in the same terminal as United. I got a gate pass from Jet Blue to meet them at the plane, and I waited in the club.
I've also used the club when arriving - usually just to grab coffee or restroom and occasionally a meeting that was called last minute around when I arrived.
I guess that would still be OK, unless arriving from a Red Eye.