This limit determines how many objects you can create in your tenant.
Objects can be created using DirSync, Powershell or the GRAPH API.
When you verify your first domain, this object limit is automatically increased to 300,000 objects.
Each tenant is only granted one increase.
|If you have verified a domain and need to synchronize more than 300,000 objects OR you do not have any domains to verify, and need to synchronize more than 50,000 objects, you will need to contact Azure Active Directory Support to request an increase to your object quota limit.|
http://social.technet.microsoft.com/wiki/contents/articles/17370.best-practices-for-deploying-and-managing-the-windows-azure-active-directory-sync-tool.aspx#A31By Amin Tavakoli