How can I know if a user is already assigned to an entity when adding them to a new one in Client & User Management?

When adding a new user to an entity, Client & User Management will now display a pop-up list of which (if any) other entities that user already has access to, and confirm you still want to add them to another entity. 

As you add a new user to an entity, Client & User Management will offer you a pop-up message to let you know if they are already assigned to one or more entities. This allows you to confirm if you still want to add the user.