I found it helpful to validate that there was something legit wrong and my 'pain' was real, rather than it just being the way I was and a diagnosis is something that can be treated, so there is hope that it will get better. My ED diagnosis was probably validating in the wrong way though and I think just encouraged me to restrict and lose weight more- now that I was an 'official' anorexic, I had to 'live up to the diagnosis' or something like that and lose ALL the weight
I have my suspicions that unfortunately my various personality disorder diagnoses have hindered the support that I've received at least once in A&E, and also considered two of the suggested "components" to my mixed PD downright insulting and somewhat confusing (how can you be simultaneously histrionic and avoidant???). I also find diagnoses that are given out after very little assessment to be quite unsettling. However, I think the final PD diagnosis I had could actually have been helpful as it gave me access to a very good personality disorder service which could have been very helpful had I chose to accept the offer of MBT.
I have rambled there; hope that answers your question somewhat!!