After last updates to MAS, system license assignment has changed. In first release of MAS, the limit will hit when you add number 30 LB/CS/VPN etc.
NetScaler Management and Analytics System (NetScaler MAS) requires a verified NetScaler MAS license to manage and monitor the Citrix NetScaler instances.
You can manage and monitor any number of instances and entities without a license. However, you can only manage 30 discovered applications on the App Dashboard and view analytics data for only 30 virtual servers without applying a license. To manage more than 30 discovered applications or to view analytics for more than 30 virtual servers, you must purchase and apply licenses.
For more information around MAS click here