As fatbrit said, the evidence suggests that aerobic exercise is fair less important to weightloss than diet, however, there is weight loss and weightloss. I think it's important to try and keep hold of as much lean muscle mass as possible. This is key to keeping the weight off in future. So exercise is very important in my opinion, especially resistance training, which suits me, as an ex rugby player I used to love chucking weights around in a gym!