If you are in the US a formal diagnosis might affect your health insurance. You should check this out if you are American.
Apart from the health insurance issue, I don't think you have to declare it to your employer, though, unless you want to. But if you don't declare it, you cannot expect any accommodations for your AS.
If you have done the AQ Test and similar scientific tests, read the diagnostic criteria and some reputable books about AS, and you are not looking for professional help (eg therapy by a clinical psychologist) then you don't need a formal diagnosis. As I don't live in the US and I was looking for therapy in relation to my unusual sound sensitivity and anxiety, I got a formal diagnosis. I have also disclosed it informally to my boss and to a couple of work colleagues that I have known for many years, although not formally to the organisation that employs me.