Why do we use resistance bands?
Resistance bands will strengthen and elongate the muscle fibers, along with increasing your flexibility tremendously. When performing a motion with resistance bands, a curve of pressure is applied during the motion, causing you to perform much more controlled motions and maintain a more consistent level of tension.
Both the concentric and eccentric (lifting and lowering) portions of the movement are emphasized. This is in direct contrast with the way many people will choose to do free weight curls, allowing gravity to do half the work; while it is possible to lift quickly and lower slowly, the culture has established an emphasis on explosion movement which is often applied to the release as well.
I recommend shorter rest periods during resistance band training, which will not only improve cardiovascular health, but provide a better workout for your muscles.