Like Michelangelo's sculpture, David, liposuction is all about the shape and contour you leave behind. 500 years later, skilled plastic surgeons understand this (see these other excellent replies). We're just trying to end up with a good shape, and aren't too worried about how much the marble on the floor weighs.
While you MIGHT see your weight change later, the priority and only reasonable expectation is to have the contour improve. It is a sculpting procedure, not a means to achieve weight loss.




