Categories are the pages within the dashboard.  But they also control access to other elements in the dashboard.

The following items are linked to categories.

• Layouts

• Charts

• Filters

• Reports

• Data Connections

• Objects within data connections

By creating categories that are allocated to different tenant's user accounts you can control everything that they can see.  You can create multiple categories for a tenant, or even share categories between tenants. It all depends on how you want to control a users access.

Roles control privileges. This allows you to control what functions within the dashboard a user can access. 

Roles can also be used to group categories together, to allow you create simple bundles of user access and privileges.