I lost all my weight with only a half-hearted, intermittent walking regime for exercise. And the first 50 lbs came off in 6 months so it wasn't like lack of exercise really slowed me down.
Now that most of the fat is gone, it's pretty obvious, at least without clothes on, that my muscles have very little shape to them. So addressing that is my current project. I find, too, that at my current size, all exercise is much easier, so that's a big boost psychologically.