You enjoy greater autonomy. Receiving a review creates a debt. Thus the author who submits a paper must give as many reviews as he receives. Editors invite debtors to review articles. A debtor who accepts the invitation must return the review within a stipulated time period or pay compensation sufficient for the editor to commission a review on an emergency basis.
Debtors have a stipulated number of years to extinguish their debt before financial penalties apply.
When an author submits an article, she has two choices. With the latter option, authors have flexibility in choosing when and what they will referee, but once they have selected an article to review, they are committed to do it quickly and well. You can even build a positive balance if you wish. Like any bank, borrowers who fail to repay are not allowed to borrow more. In this case, that means no further submissions from a defaulting borrower will be accepted.