I am in the Rarely camp. A year or so ago I tried it a few times after watching a Muttnchop Piper video on dumping ash. Since, I tamp more and lightly, and occasionally stir the bottom 1/4 of the bowl. I either dump the bowl when it is finished and mostly ash, the bottom of the pipe gets hot, or the smoke is tasting like ash. While I don't like wasting tobacco, life is too short for bottom of the bowl smokes that taste of fireplace. Like most pipe smoking, it's a process and evolution.
To expound my habit: I keep the charred disc on top, and continue to tamp that as the tobacco is consumed. The only thing that is dumped is the loose ash. For me, it beats trying to ignite the bottom of a bowl full of ash.
A well packed bowl, properly lit, tamped and smoked, I can turn it upside down and only loose ash falls away. I find the taste becomes muddled when keeping the ash. By slowly sipping I get a cool burn and preserved flavor.
I do dump occasionally when I feel like the bowl is having trouble staying lit. Inconclusive whether or not it helps. Sometimes I kick off the ashes when they’re making a mess - since I smoke outdoors that’s an easy puff over the top of the bowl or a flick of the wrist. When I’m planning on taking a dump I always insert a pipe cleaner to make sure no dottle finds it’s way back into the bowl, then I flip out the ashes, then remove pipe cleaner and tamp back down and relight. Like most things about smoking a pipe, there is no hard and fast rule for when I do it nor am I sure it even helps but hey - I’m smoking a pipe for my relaxation and enjoyment not for the aesthetics.
I too am in the sometimes camp, particularly in chimneys or stacks. I angle the pipe and allow the loose ash to fall out, then tamp lightly. I tell myself it allows me to sip more slowly and aids in any relighting.
So this is something that has happened to me. Since I’ve basically never dumped, I’d get to the bottom of the bowl and have some ash fly up the stem right into my mouth. You’d think, ah, it’s done. Nope, I dump and there’s quite a bit of unsmoked goodness.