Controls maybe, but I disagree with the notion that it "moves first."
I don't think the tanden powers it so much as controls.
Motion should still iniate from the legs.
Anyone else want to chime in?
I'd say it depends a lot on what you're doing and what your goal is. Most would agree that whatever movement happens, it will initiate separate from the point of contact. Beyond that I don't believe there is or should be a hard and fast rule where you always need to move from. This is one thing that newaza really hammers home. If you only know how to root from your legs, you're screwed. If you need to begin all of your movements from your hips, what happens if they're trapped? I think it's actually more important to know how to move intentionally, stabilizing some areas of the body, and intentionally relaxing others all while maintaining sensitivity at whatever points of contact you have.