It depends on the throat of the gun and how tight a fit the slug is, whether or not you have to clean between shots. The blowing softens the fouling and presumably helps accuracy. Most people use a piece of 1/2" plastic tubing as a blow tube, others such as me use a piece of copper pipe with a bit of a bend in it. You have about 6 minutes for 5 shots and as long as you are organized that is long enough.
In a muzzle loader it would soften the fouling but on trail walks where you are firing 25 or 30 shots, you also normally use a water based patch lube and that more or less wipes the bore with each loading. Coarse powders and greasy lubes will dramatically increase fouling and probably force you to clean every few shots.
cheers mooncoon