|Users, Groups, and Permissions / Working with Permissions|
The Revoke button cancels a permission that a user would otherwise have by virtue of membership in another group.
You can revoke a permission to ensure that a group of users does not have a specific permission, even if membership in another group grants that permission.
For example, if your site issues courtesy badges to visitors, you can use Revoke to make sure that visitors do not have certain Vocera permissions. Suppose the Everyone group grants the Call Toll Numbers permission. Because Vocera automatically adds all users to the Everyone group, visitors are also granted that permission automatically.
To disable this permission for visitors, you can create the Guest group, then revoke the permission for Call Toll Numbers in it. When you add all visitors with courtesy badges to the Guest group, they will have all the permissions granted by membership in Everybody except Call Toll Numbers, which is revoked by membership in Guest.