I have not used sealer over completely primed panels in years. If it is a primer spot on a panel, sealer is a good "insurance". If the panel is primed complete, it is a waste of time and money.
I used sealer on every job I did, but haven't now in years.
I stopped after the first trip to a tech school put on by a paint company. Now, the first thing you will hear from the masses is how the paint company just wants to sell products, be damned with if they are needed or not, right?
Well when the subject of sealers came up, he had writen on the board the part numbers of the company sealers and then asked why do we use sealers?
He put a list up on the board as answers, "Too coarse of sand paper used", "Poor hiding colors to be applied", "1K primer was used", and many more. They were ALL related to poor product choice or improper prep work. He then explained how the 2K primer (be it urethane, epoxy or whatever) is insoluable and you just don't need sealer over it.
I haven't used it since.