Repacking exhaust?

How and when do you know to repack the exhaust?

http://www.vfrdiscussion.com/forum/http://www.vfrdiscussion.com/forum/index.php?showtopic=5780

Is there a certain number of miles that it needs to be done?

When the sound turns bad, miles be damned its a sound quality issue. Nobody rides the same so miles are not an issue. You dont have to repack a stock exhaust btw. They dont use packing, I replaced my old D&D with a Staintune which never needs repacking!!! If you can find ceramic packing fiber use that instead of fiberglass its better and will last longer if packed tightly.

I read the How To guide. HS uses stainless steel wool around the perforated pipe to prevent blowing a hole in the fibreglass (or ceramic).
I have had a look at the Staintune website. They use stainless steel wool. There was a post here recently of a BMW that had Staintune muffler installed for 20 years (if I recall correctly) & it was still perfect.
Why not repack the entire muffler with just stainless wool?

EDIT: I think I am answering my own question after thinking about it. The CF Staintune muffler uses fibreglass packing & has to be re-paked. I suppose stainless conducts more heat to the cannister outside so the outside is much hotter when packed with stainless.
Next question: If stainless packing is used in a CF exhaust does the increased temperature break down the epoxy and destroy the can?