Brasso is a cream abrasive. Be very cautious what type of barrel you do this to, and how often. While you may be removing any scratches and creating a higher polish on the inside, realize that this is done by using abrasion to polish out the finish. ie, you are performing micro scratching. Do it a certain way for a long time, and you will eventually open up the bore - and if doing it by hand, don't expect the wear to be 100% even on all sides. You can develop an uneven bore, which could be worse than a rough surface.
There are less destructive methods to cleaning your barrel. Using cream abrasives is just the fastest/easiest way to do it. You pay a price for it over time, though.