Had a positive experience with same-day GPU usage. EWR-SFO was booked 16/20 in F when I OLCId to #1 on the waitlist, eventually slipping further until I was #3 on the list with 19/20 booked. (I do believe that higher-yield pax are stereotypically busy folks and tend to check in later.)

Went to the UC at roughly T-90 minutes and asked if I'd have a higher position by applying a GPU. Inventory must have been F1R1 (I hadn't checked), but within 30 seconds the agent was able to confirm me into the last F seat. Well worth the GPU given that I have no paid overseas travel this year. ^