From the customer perspective paying month creates an ongoing incentive for the developer to continue to maintain and enhance the offering. If the application i

From the customer perspective paying month creates an ongoing incentive for the developer to continue to maintain and enhance the offering. If the application is something that you would foresee using every month, or at least most months, then paying for it monthly aligns incentives. From the seller perspective it is normally easier to get folks to pay a smaller amount for one month's use than an annual or perpetual license fee. You can always offer annual and multi-year licenses with a discount structure in addition.