Under Roles>choose action, there is only the option to 'apply roles' to a group of selected individuals but not the option to remove roles from selected individuals. So if an IT admin made the mistake of assigning a 100-1000 users the wrong role, he/she will now have to go through each one and remove the role manually. If the drop down has the option to apply a role to all selected users, it should also have the option to remove a role to all selected users.
A good example of when a situation like takes place is when many IT admin use the default User role when assigning to its users. Usually several months pass before they realize they want to hide some of the tabs within the UserUI role. However, if they are using the default User role, they cannot save changes and must create a duplicate just to save the customizations. Now they are stuck with having to remove the old role from all of the users and applying the new role. This can take a very long time if they have 1000s of users with the current method. However, it would go by much faster if they could simply click the box to check all users on the page, then select 'choose action>remove role', save. Then 'choose action>add role', save.