They are useful if they are understood properly. For example different "similar" groups respond to different treatments differently. Social phobia responds very well to exposure therapy, anti-social personality disorder does not. If you are able to follow the distinctions you are able to leverage more effective treatments. I don't think they have any use outside of psychological treatment though. This is a great video on a good way of breaking down how personality disorders in general are broken down and function and are separated. https://youtu.be/4mgifm3ftl8