I havent tried this on purpose but I have noticed that when I smoke slowly enough that I have to re-light several times during a bowl, each time I light the tobacco it is a little richer and the smoke a little heavier. Some mild tobaccos could improve using this technique I think. Theres nothing worse than pipe tobacco that is too mild, you tend to over puff and make it hot and bitter.
Thanks Bob, I thought I didn't get it because I was a geezer. I like to smoke slow if I can but that never works for me. I huff down a cigar and rarely smoke it slow. Once in a while I come back to a half smoked cigar but I don't realize any improvement over that nor did I when I smoked a pipe.