In reading a lot about this it seems like a lot of controversial things can impact accuracy in AR's. Not surprising given all that can impact accuracy in a bolt gun (action screw torque, bedding quality, etc.) Probably partly controversial by the very nature most people can't shoot them as well as bolt action guns due to the mechanics. That said if you read lots on what the guys do that build competition uppers, and the AMU etc. you frequently hear them talk about the same things like bedding the barrel extension, facing the upper receiver, either hand picking upper/lower combos so they are super right, or bedding them, hand fitting gas tube alignment, not pinning gas blocks, using a heavier upper than mil-spec, using a super rigid handguard, ensuring front to back bolt play tighter than spec, etc.
Ask a precision rifle shooter to loosen his trigger guard or trigger screws, or action screws and shoot groups and they'll look at you like you are crazy, to me this isn't that different.
Some might say those things are useless, but at the end of the day I've always been in the camp that if they don't hurt anything, there's no penalty to trying them aside the time it takes, and if they help even a little bit it's worth it. When it comes to precision having things loose is almost always worse than having things tight.