Finally.....somebody asked the question!! Personally, based on my experience with it, I have to conclude it is marketing, albeit clever. I have been unable to see any evidence where it is any more accurate, shoots better or fouls less/cleans easier. Wish it did all of the above, but no. I have even tested it in handguns shooting cast lead bullets and still...no.
A little background on why the Russians used it might be in order...it is my understanding that they shoot mild steel jacketed bullets {I guess copper costs too much or is "rare" there} and initially found that this caused the drive side of the rifling to wear prematurely, especially when firing full auto. So, the cure was to make it that way, that is with a "ramp" or radius on the drive side and hard chrome the bore.
Along comes some clever folks that "Americanized" it and here we are...everyone thinks it's the final word in the matter of rifling.
When enough people thought they had to have it, which was some years ago, many barrel makers started to offer it. Krieger held out. They had a pretty good write up on their website for quite a while in which they discussed testing and being unable to find a single advantage or even difference. So, they didn't offer it. Sales must have finally suffered enough to cause even Krieger to jump on the wagon and start, because now they do.
I say it is marketing because that is where it really works, shooting wise, not so much so. If I were going to build a custom rifle just to sell it would have a 5R barrel for sure. It sells.
Edit: I have had a few 5R barrels that shot great, but no better than the others with conventional rifling. I will say this, the two absolute worst fouling barrels I have ever owned are both 5R's and from two different manufacturers. Both are cut rifling and both have been shot long past the so-called break in period.