It is always interesting to learn how Microsoft uses their own product in an Enterprise environment as large as Microsoft. Lesson can be learned from their effort.
How Microsoft deploys Windows 10 and implements Windows as a service internally
"Learn how Microsoft adopted and deployed Windows 10 internally using Enterprise Upgrade as the primary deployment method. This approach reduced the deployment overhead by using System Center Configuration Manager Operating System Deployment (OSD) and upgrade which resulted in significant reductions in helpdesk calls. In addition we share how we are leveraging some of the new enterprise scenarios to delight users while securing the enterprise. You can realize similar benefits in your enterprise by adopting these best practices as you migrate from Windows 7 and 8.x to 10."