William Glasser, the founder of Reality Therapy, said, "...we who practice Reality Therapy advocate dispensing with the common psychiatric labels, such as neurosis or psychosis, which tend to categorize and stereotype people; ... the label thereby serving to compound the problem."
I agree. While the diagnosis has value as an unhealthy pattern, it does little to help a person in therapy. In fact, as Dr. Glasser says it often gives the person a further excuse to avoid responsibility for their actions.
In Life Patterns, we find that the same pattern has healthy and unhealthy components. We work with the healthy side of the pattern, and, even though a disorder, which is an unordered, non-specific approach to problems exists, it is still a pattern. If it was not a pattern, no one could make it into a diagnosis.
The question is does the diagnosis help in psychotherapy, I don't think so. Knowing the pattern helps. If the client understands both the healthy and unhealthy aspects in the pattern, they can choose which side of the actions and thinking they want to use in life.