It’s a good read to get started and gives you some talking points to discuss with your reseller & Microsoft account manager.
One key point to note is that this means that on July 1, 2016
… the minimum Enterprise Agreement (EA) commitment for commercial customers signing new Enterprise Enrollments or Enterprise Subscription Enrollments will increase from 250 users or devices to 500. Along with this change, we are guiding new commercial customers within the 250 to 499 user or device range to our modern volume licensing solutions: the Microsoft Product and Services Agreement (MPSA) and the Cloud Solutions Provider (CSP).
For those who need some more time to adapt to the new situation and who’s needs don’t get served well by the Microsoft Products and Services Agreement (MPSA) and the Cloud Solution Provider (CPS) offerings there is an option to extend the existing EA for another 3 years. That might well be worth doing.