Think about this for a second after you read it and you will understand why I always sand, finish and polish the inside of my trumpet calls.
If you had to drag a 100 pounds of something/anything either over a smooth, finished and polished surface or over a rough, jagged unfinished surface, which surface would it be easier for you to drag the weight over???
Sound is no different, it will flow much easier over a sanded, finished and polished surface than over a rough, jagged unfinished surface.
Does that make sense?? Just my thought on the subject.