A role is a predefined set of privileges. Privileges define individual rights that a user requires to perform actions and read properties.
When you assign permissions to a user or group, you pair the user or group with a role and associate that pairing with an inventory object. A single user might have different roles for different objects in the inventory. For example, if you have two resource pools in your inventory, Pool A and Pool B, you might assign a particular user the Virtual Machine User role on Pool A and the Read Only role on Pool B. These assignments allow that user to turn on virtual machines in Pool A, but to only view virtual machines in Pool B.
The roles created on a host are separate from the roles created on a vCenter Server system. When you manage a host using vCenter Server, the roles that are created through vCenter Server are available. If you connect directly to the host, the roles created directly on the host are available.
vCenter Server and ESXi hosts provide default system roles and sample roles:
System roles are permanent. You cannot edit the privileges associated with these roles.
VMware provides sample roles for convenience as guidelines and suggestions. You can modify or remove these roles.
See Roles in vCenter Server and ESXi for information on creating, cloning, and editing roles.
All roles permit the user to schedule tasks by default. Users can schedule only tasks they have permission to perform at the time the tasks are created.
Changes to permissions and roles take effect immediately, even if the users involved are logged in. The exception is searches, where permission changes take effect after the user has logged out and logged back in.