Not wishing to be contentious, but smoking down to white powdery ash is not, and never was a goal, for me. I generally dump out the last shreds of tobacco when they lose their ember of life, and go out. In fact, I never really think about smoking all the way to the white-ash stage when I smoke my pipes. If it happens, it happens.
Relighting, and almost forcing myself to smoke a few shreds of burnt, rank, dottle, is not my idea of how I want to end a smoking session. I despise coating my tongue with bits of burnt tobacco and crispy ashes. I would much rather call it quits and cut my losses.
Charring relights -which are almost always necessary- with a scant minimum of tobacco at the bottom of the bowl.....can cause the heel of the pipe to burn out, or worse, crack, from the excessive, raw heat and flame. Why take that risk just to smoke a few shreds of soggy, used up tobacco?
That, being said, there were very few times that I actually got to smoke down to the bottom of the bowl without any relighting. My Muse of Pipe Smoking must have been hovering over me on these occasions.
But I am never unaware when smoking, that there is a certain magical point, where the flavor from your fresh charge of smoldering tobacco changes, and it goes from good to not so good, then to bad, steamy, and rank. At this point....the party is over, for me. I call it a day, dump the shreds, and move on. In my world, white ash at the bottom of the bowl is as rare as the truth from rat-face, Dr. Fauci.
Sadly....my pipe tobacco is not like a mythical Phoenix.