I hope you don't do it for every overhaul of frame that has been faced properly once. Once a frame is properly faced, it should never need it again unless it is repainted and then only to clean up any overspray.

All repeated facing accomplishes is to narrow the bottom bracket shell until the bottom bracket doesn't fit properly. Do it once (only if needed) and leave it alone after that.

My experience mirrors DaveSSS's. I've built up three Litespeeds Ti frames and a Co-motion steel frame from scratch as well as bottom bracket replacements on several other bikes and none of them has needed facing.