Urethane sealers are good for an even color and handling scratches that you missed, if coated in right time frame perhaps they give a little extra chip resistance.
My personal feeling is if primer sanded right and its an insurance job, no big deal either way.
Epoxy as a sealer is the best of best, I know of no restoration or rod building shop that don't use it as they have to live with these high dollar jobs.
For 15-18 years one of my jobbers has sold and insurance shop, he is direct with 9 insurance companies and has 4 painters, he will not take a car over 5 years old and the insurance companies love him as like he says, they never get a complaint.
Ten or so years ago, he asked me to come buy as certain cars would get chipped up in the front end if they drove gravel roads or expressways everyday.
My answer was to stop this, use epoxy as a sealer, now that is a real problem time wise in a shop like this but he took me at my word.
It stopped the problem! Hands down!
Then about 3-6 months ago he called said I have had three cars come back chipping, I asked with epoxy sealer? He said no, these were real rush jobs, I said any come back with the epoxy as a sealer, he said no.
I said well guess we know the answer, he said yea, just need to bitch at someone. LOL
So bottom line is if the car is just a used car special or just want it the same color, save money and base over primer.
If car is something to be proud of and want to last use epoxy.