Why, you ask?
Well, Mark Bittman told us to do it, of course, and who are we to turn down his advice?
Grinding your own meat sounds fancy, but it's actually quite simple if you have a food processor. It also brings several benefits -- especially the fact that you know exactly what meat is in your hamburgers.
This recipe, from Cook's Illustrated, adds an unexpected step that really takes burgers to the next level: freezing the meat slightly before you chop it.