It's been mixed for me -- mostly used between LAX and ATL or JFK. Mostly to the gate but the odd one has cleared in advance. I "wasted" two that were going to expire on LAX-SEA and back (as part of an LAX-SEA-AMS back when TCONs needed GUCs)

I am waitlisted on JFK-LAX on a Sunday evening in early May. Exactly one seat up front is gone according to the seat map.