There's something very intimate about drawing. It allows me to explore my subjects and models in a way I don't often experience with paint and brush. Before I begin a painting (especially a major piece), I often work out a dozen or more of these quick graphite studies. That way, I understand potential problems and can often mitigate them before painting myself into a proverbial corner.
That being said, I probably draw more for the shear joy of it than any other reason. It's just plain fun! I've always admired those who can accurately convey a thought, concept, or image with sure-handed strokes of a pencil. Even the most elegant graphite drawings still have an earthy, almost primal feel to them. Still, I find the quick studies found in artists' private sketchbooks most appealing. The drawings not meant to be a "finished product," but to serve as a visual note taking process... those are the ones I never tire of seeing.
All you young artists out there... NEVER STOP DRAWING! There is absolutely no substitute for good drawing skills and it's easy to spot those lacking in this department.