Health reasons, I also want to have more energy, which I know can be achieved by exercising more often, but of course, having less weight to drag around would help a lot, too.
The other reason is that the last time I've been "normal" was before I hit puberty, aka around 8-y old. I'd like to know, in my adult life, what it is to be "normal", and not "overweight/obese". I find it sad that I don't even know what my normal weight would be, since I've never been there after having stopped growing up... *sighs*