There is some evidence that the gentle compression of the wrap on the belly may help the uterus to return to its normal size earlier, making the belly appear smaller.
When used, they can also help you fit better into clothing, but there is no evidence that a belly band reduces tummy size.
Ultimately, a good and healthy diet combined with exercise will help you shed off the pounds.
http://www.webmd.com/baby/features/belly-wraps-post-pregnancy-hit-or-hype