Fire Lapping has its merits
As a former Benchrest Shooter it is my opinion that firelapping has its merits and is used by some Benchrester Shooters although it seems to have fallen out of favor over the last few years.
I don't believe that it would really benefit the average AR Builder using combat grade Bbls. Unless you are trying to build an AR capable of consistent sub MOA groups consistent then the process is more trouble than it is actually worth. Keeping in mind that while we may put thousands of rounds through our Bbls, the life expectancy of a competitive Benchrest bore is only around 2000 to 2500 rounds.
I have heard of some shooters who have Fire Lapped a Barrel trying to rid it of the (Alligator Hide Effect) which appears in a barrell having many rounds ran through it, or to loosen up an obviously tight bore.
I have always used the one shot clean method to break in a new barrel with good results. I have a Remington 700VS rechambered to .22-250 Ackley Improved that shoots in the 3's consistently, with a best group of five going into .248". My old 700 BDL Varminter is .223 Rem shoots almost as well, and both will hold minute of crow out past 300 yards.