A roach actually is marijuana left in the end of a joint/blunt/spliff after a smoking session. A roach is not the crutch used to make a blunt more "breathable" or the paper left over after all the weed is gone.
If there's no herbal left in what you're smoking, you might as well toss that shit. My roaches are normally half an inch to an inch long with no crutch-- at least 0.1g-0.2g apiece. If you can't salvage any bud from a roach then there's no reason to save it because at that point all you've got on your hands is paraphernalia, not drugs.