I believe that breaking in simply saves more barrels than it helps shoot well by making the shooter take his time.
I have seen new (a year or two old) rifles that couldn’t hit the broad side of a barn. The owners would complain and gripe about how bad it shot, how the POI changed, and anything else that they could think of.
Well one day on the range observing some of these shooters tells the tale. I don’t know how many times I've seen guys with sporter and light sporters in say 30-06, 270, 7mm REM MAG, 243, among others, sit down and shoot and shoot and shoot and shoot, and 20 rounds later, moving their reticle with every shot, announce that the rifle is junk or the ammo is junk or the scope is junk when in actuality their knowledge is lacking.
I sat by one of these yahoo's one day and just watched the heat rise from his barrel, when he got all ticked off at his rifle for not grouping I said "hey, I think you might have it a little hot" he looked at me like I was a stupid kid as I was at least 20 years his junior. He said "it aint that damn hot" reached up, grabbed the barrel and screamed. I laughed and said "see, I told you it was a little hot" he never answered just packed up his stuff and left.
So does breaking in help, I think it all depends. I think your actual method of shooting and general care does more for your accuracy than your break in procedure.
J.