It's a training step for the eventual, ultimate goal of yelling at a 50-gallon wheeled trrashcan. Scientology is just a front for the garbage collectors' union.
Not many people know this, but when you smoke, you're actually exhaling a tiny piece of your soul. That's the real reason it's fatal: the smaller your soul becomes, the less your body can sustain itself. Parts of this soul-energy are absorbed into the cigerette ashes, which are then collected in the tray, which then assimilates the energy from the ashes themselves. By yelling at the ashtray, scientologists can coax the collected soul-energy to reveal itself. Then they harnass that energy to power their massive unearthly mind-control device, in hopes of one day collecting enough energy to make Tom Cruise like girls.