BB shell "facing", IF needed at all, is only needed once. Basically, it's to make sure the BB shell is 'square', not lopsided on the exterior contact points with the external BB. The more expensive the frame, the more likely it was factory faced.

Most often, the "facing" only clears sloppy paint from the frame. Did that myself once with a file, had no issues.

ONE of my last three frames could have used the facing operation, and only for the external-BB crankset. I've been using an ISIS crankset for two years now, and IMO, it's better than anything external. ISIS and Octalink is where they should have stopped.