Not everyone has listings on the market all the time. And sometimes you could go for a few months (or more) with no listings on the market.
This is why ShowMojo has Annual Plans (and, more recently, multi-user annual plans). With an annual plan, an account can purchase up to a year's worth of leads and usage at a discount rate, leveling out periods where you would not otherwise need ShowMojo.
Additionally, when you upgrade from most monthly plans to an annual plan, the payment for the current month is credited to the upgrade, effectively reducing the cost of the annual plan.
Current customers can upgrade to annual billing plans on their Billing Settings page.
Unfortunately, Showmojo does not have the capability to outright pause or suspend billing on accounts. Even if an account is not in active use, there are still some real expenses against it.