Hello James.
My personal perspective on diagnosis.
Pros: Greater insight into and understanding of some personal traits and idiosyncrasies, decrease in self-imposed pressure to be 'normal', acceptance of some otherwise troublesome aspects of your personality, justification for explaining your social differences to friends, family and acquaintances, a measure of official recognition of any needs you might have (including access to benefits such as Disability Living Allowance), official recognition of Aspergic communication modes and characteristics by local government and health bodies (under the Autism Act (2009)), you will also become a person with protected characteristics within the terms of the Equality Act (2010) meaning that employers/educators and other service providers are required to make 'reasonable adjustments' in order for you to cope in that environment.
Cons: When you disclose your condition to others, they may be scared off, or have stereotyped ideas of what your condition means (without taking your personality into account), and in some cases antisocial individuals may actually seek to victimise/harass or otherwise manipulate you by exploiting your characteristically-Aspergic social naivete. Also (and this is based solely on my personal experience) you may find the diagnosis psychologically-limiting, in terms of your perception of your own abilities or personal developmental potential, and this can lead to negative self-image, self-defeating thought-patterns or into outright depression. It can also lead to (consciously or unconsciously) self-indulgent behaviour in which Aspergic traits are expressed to the detriment of one's socialisation (e.g., thinking: "I am bad at this aspect of interaction, so I won't even try")
In all, I have found diagnosis to be a mixed blessing, although it finally provided me with a suitable framework within which to address some of the persistent questions about myself and my relationships with others, that had bothered me since I first became aware of my slightly-disjointed behaviour and unusual thought-patterns.
I had reached the stage in my life in which I felt I needed firm answers to my suspicions about myself and thought I was psychologically-ready to receive them. Perhaps displaying a characteristically-Aspergic lack of social imagination, little did I imagine that I would in fact be faced post-diagnosis with a whole new set of problems, challenges and dilemmas.