I make it habit to purge my cigars real often while I'm smoking, just because I like to smoke them "clean". I don't like the "dirty" flavors that build up in a big stick. I don't notice it so much in little ones, but I purge them a bit out of habit.
By purging along the way, it takes a little longer for the backend flavors to develop, but I like them more and I don't get any ashtray flavor.
Mind ya, that's just my preference, enjoy what you like how you like it.
On the tar, you got your answers. Slow down, purge, and fix the cigar if you have to. Slowing down and not letting the cigar get hot is probably the best way to control it that I know of.