The Microsoft Services Provider License Agreement (SPLA) is a licensing program that provides a hosting offer to service providers and ISVs to lease or rent licenses of Microsoft products on a monthly basis, and to provide hosting services and applications to the end customer.
If you require 2 licenses this month, you pay two licenses, but if next month you use 30, then you will pay 30 and then you can go back and pay only the 2 initial licenses or the amount you need. There are no minimum or maximum quotas.
With SPLA, Microsoft is investing in the success of their channels and treating the software as a service "pay-for-what-you-use" allows them to increase their flexibility, accelerate profitability and establish a recurring revenue model to expand business. In addition, this program makes software costs transparent to end users, who may also treat the software as operating costs rather than capital.