Cigr, I've seen my uncles do the ash thing, way back in the day. It makes a fluffy soft cake, especially for someone who smokes a lot of those burley based codger blends. But, when that ashy cake gets wet or left in a humid air, it swells up, and can break the briar. And, it's more prone to breaking off leaving the briar exposed in areas. I've seen pipes where the cake has swollen up and actually protruded out of the bowl. This was from the days when guys smoked their pipes till they were just too nasty to bare, and then they'd toss them in the fireplace.
Also, cake makes your pipe smoke cooler by insulating the briar, but you're only making it cool to the touch, not cooler on your tongue. If you can't smoke your pipe cooler by smoking slow, then you might want to consider a pipe with more mass of briar around the chamber. But, heck if you want cake, do it. If you want a massive cake, do it. It's your pipe. Do what you want.