That's how you create a notch in your workpiece using a dozuki. If all went according to plan, all its teeth should still be intact, and you should have a rectangular section of wood missing from the workpiece.

Remember: the dozuki blades are replaceable. There's no reason to throw away a dozuki if the teeth snap off. In fact, you can grind them off and use the old blade as a scraper! (Thanks Mr. WoodMan!)