I stopped burning off rubber band goo and stuck-on labels a looong time ago. Pretty early in my newbie days I discovered that it does not burn away completely most of the time. It is easy to see what impurities remain with transparent glass especially, and it shows as tiny microbubbles where the gunk was. Since I am not 100% sure the stuff burns away completely, I don't take chances. I have had beads crack around the holes where tiny flaking bits of bead release got into the glass and melted in. So I don't want to take chances with possble remnants of ash residue inside my beads which might cause incompatibilty issues.
Maybe I worry too much, but I am not alone in believing that glass needs to be cleaned thoroughly to avoid incompatibility problems. It is better to be safe than sorry! A good way to go through life.
