My buddy, who in general is to be trusted on such things, is claiming that you shouldn't smoke what-i-would-use-as-the-last-two-or-three-tokes of a bowlful. He's saying that it's already been heated, the stuff you want has been vaporized and inhaled, and that you're just taking in two or three lungfuls of nearly useless smoke. He dumps his bowls way before I ever do. What do you think? Can anyone provide hard facts?