I have heard bands have to pay back the label for studio budget so album sales are pretty important. A label or band is going to try hardest to sell their cds. If a band could not pay back studio costs a label probably would not keep them for long. Albums sales is not extra money for a band unless they sell enough where the can pay back the label and have extra money. You also do not know how much a label puts towards touring,gear,etc.... or if they want you to pay that back with album sales also.