Since I first read this and after my response I've been thinking about it off and on. I'm 68 and retired...not a lot to do in the winter lol and my Zwift race doesn't start for 2 more hours.
When I worked in a bike shop back in the mid '80's to early 2004 I seem to remember not having to 'face' many bottom bracket shells. If I remember correctly all the bottom brackets were internal bearings...in a cage or the better ones, loose bearings...and the race shells were near flush with the outboard face of the bottom bracket shell on the adjustable side. The fixed side would get faced. Generally this was done on steel frames...which most were...because of the paint and top coat. This needed to be removed for a flush/flat fit of the fixed bearing cup. Same on any frame that was painted. We always faced the head tube. We always chased the bottom bracket threads just in case there was overspray. You certainly don't want to cross thread a bottom bracket...yikes it is not pretty but it can be saved with patience, effort and prayers/offerings to the bike gods. We generally chased all threads just because it was the right thing to do when the bike is being built and a lot easier to do then than later...which may mean a cross thread problem.

Most bike shops build far more "bikes in a box" than "frame in a box" during the year. They also come nearly complete so the bottom bracket and head set is already installed and generally don't need adjusting. Sometimes when replacing a bottom bracket we may find the fixed cup side was never faced...it happens...then we would face it because we had the tool, likely hadn't used it for some time...woohoo we get to use a cool tool...and/or we had a new mechanic who never used one before...learning opportunity. We did the same with a head set replacement...this was back in the day when the 1" threaded head set ruled the world...none of this 1 1/8 new fangled technology...if a 1" threaded head set was good enough for EddyM it was good enough for everyone...oops forgot what I was talking about...I'm old, I forget...

Titanium, Carbon fibre, etc. frames don't need facing...and honestly shouldn't even require a check "if" built correctly. I got an Aethos a couple of years ago and it was perfect out of the box. Same with the Tarmac SL7, SL8, Carbon Diverge, Roubaix and Crux I've built in the past year or so. Perfect right out of the box.

I'm still working in a bike shop, part time of course, and I've not used a facing tool in years...but we gots one.