I understand the OP's skepticism. I use the confirmed standby benefit very rarely.

- I nearly always book the flight I want rather than a cheaper one later in the day. I prefer the certainty of knowing I'll have a convenient schedule rather than risking it to save a few dollars.

- When a schedule change results in my arriving early at the airport, my experience has been that earlier flights are nearly ALWAYS booked full. YMMV.

- On the rare occasions when the earlier flight isn't full, typically I've found that F is already full and only E- middle seats are available. I'd rather wait.