I've never had a problem with an uncoated bowl starting any burnout process, so it mystifies me why coatings are used. Apparently, uncoated bowls cause enough returns and complaints that the expense of a coating benefits the pipe maker. Few if any artisans use coatings, in my experience. I don't bother sanding out coatings, but I award points for pipes that don't have them. I haven't kept track, but it seems to me some factory pipe brands coat some pipes and not others, which is another mystery. Presumably, beginners are at the most risk of burning up a pipe, so perhaps they are the intended audience for coatings.