I don't know about JAX, but for LAX I would say it is worth it but it may not be open at the time of day. I had an early morning flight out of there once and I left earlier than I thought I needed to in case there was traffic. There was no traffic but the line was not only absurdly long at 4:30AM but it was weirdly snaked around and almost out to the curb. Another time I had an afternoon flight and the traffic was absolutely ridiculous - not getting to the airport - but entering the airport. It took 30 minutes from the time the Uber turned onto the airport drive to get up to the entrance. But thankfully the priority lane was open that day and it saved us.