Why is hip position so important in BJJ?

One of the major goals in grappling is to get your opponent's hips to the mat and keep them there, while keeping your own hips off the mat. For sweeps, takedowns, wrestle ups, and most submissions and dominant positions, you need your opponent's hips on the mat. Constantly popping your hips up and off the mat is an effective way to defend. Do not do work for nothing - finish by pinning their hips.