I hate smoking through clogged pipes and then you get a buzz from oxygen deprivation.

It is best to clean the pipe after each use. Something I never do but I also don't let them go that long before cleaning. That left over tar (seems to be the theme of the day) doesn't burn away completely but everytime you put a flame to it, some of it burns. The more tar at the bottome of the bowl, the more harmful by products you may inhale.