I agree with Big Al. However, if you are currently "fat", IE: more than 25lbs overweight - you could gain more due to having a stronger erection.
Some people get fat enough where they are more depressed and also have worse circulation.
So losing the fat, getting into good cardio health will remove your depression or having you closer to your mental and physical peak. It will also improve your circulation.
So you might be surprised to find your erections are harder, fatter, and of course the loss of fat pad exposes the penis that was covered by it.
I know, because I've done it.
So I say, you gain a bit more than uncovering the fat pad.