There's still moisture in the mortise. A good clean out after a day's use will take care of that and help keep your pipe sweet.There's another benefit to smoking to the bottom or very nearly so: When you're done, the briar is dry. The heat from the ember dissipates the moisture and the heel is no longer soggy. Ready for a pipe-cleaner and time to reload! This would seem to reduce or eliminate the need to rest the pipe for any period. Though resting a pipe regardless of moisture in the heel seems a natural thing.