Cajunboy,
Yes there is a benefit.
The residual machine oils and grit are present after the build.
Also,you have a doubt or you wouldn't be asking the question.
Take 20 Min,punch the bore untill the patch comes out white,and scrub the upper and bolt carrier group untill you are satisfied.
Apply your trusted lube and then go break it in.
The amount of machining grit and such is really not that detrimental,but the psychological impact of doubt is.
Shooting is 90% between the ears.
Treat the rifle as you would your own self,and go on about the process in confidence.
Don't sweat it.
You should see the contortions I and some others go through with a new rifle.
Just do what you feel is right.
Remember that those folks that take the lazy approach and never consider such things are often those that wonder why stuff goes wrong.
Keep sharp and never be afraid to ask or share!
S-28