Building muscle mass is a combination of an overloading stimulus and sufficient rest to allow the muscle to heal itself. If you skew this balance either direction, either working out too much or providing too much rest in between, you aren't going to get optimal results.
The more frequently you are able to work a muscle though (assuming full recovery has been achieved) the faster you will add additional new muscle. Cardio helps you do this. Just don't take this too far as excess cardio or cardio done at such a high intensity that it places additional strain on the muscles is going to actually hinder recovery rather than aid it.