I've heard of baccy being used as a filler but never tried it myself. Seen god knows how many threads here about it though. From what little I understand, I think you're supposed to toast up the baccy to cook some of it off. When I watched a dude do it, he put some in tin foil and lightly roasted it with a lighter. None of it really burnt, but it was a darker lighter tasting product that kept the blunt from being too harsh.

I'm with lip, I think it was 1st used to add some filler to hash and there's really no need to mix it with weed, but anything could work as a filler. It just depends on how much cancer you wanna get. Baccy is bad but still better than some pine needles or sawdust (as far as taste goes).