Smoking a mold puts a thin insulating film on the cavity surfaces. And a fragile film at that, which wears quite rapidly. The reason Lee molds need it is because there is chatter in the cavities and the cavity edges are not deburred at all. The thin film is enough to help bullet release. The insulating factor, helps bullets fill out better in alumiinum or brass molds, which draw heat faster than steel or iron. I stated that the film wears rapidly, but the downside is it doesn't come out evenly, so after several applications the sharp corners in the cavities get a buildup that changes the bullet some.
I prefer smoing with a butane lighter rather than matches, as the smoke seems a bit cleaner, and it doesn't quit before I'm done smoking the whole mold. Always heat the mold to at least boiling temperature before smoking so the steam in the smoke can't condense on the metal between and with the soot, which will cause the soot to come off quicker. The flame will not deposit soot unless it is in contact with the metal, so hold the lighter or match close to the mold.
I don't recommend smoking LBT molds, because the cavities I cut are very high precision, have absolutely no chatter to lock bullets in, and I debure the cavity edges very carefully, enough so that a fine line is visable around the bullets if the alloy is runny enough. Carefull deburing is mandatory for a mold to have good venting, and good venting is mandatory if the sprue plate fits flat and tight and the sprue are small. The only venting on lee molds is from under the unfinished sprue plate and through the huge sprue hole.
