How necessary is head tube reaming and facing?

I have never had it done on any frame and never had a single headset issue. And that is combined with me banging the cups in with hammer and wood!
It is not something I would even think of having done.

Probably not best person to answer though as I never keep my frames long enough to see any headset issues :-)

I tried this once but it left deep marks in my wood. So now I use a rubber mallet.