Because pretty much every man and his dog has some from of higher eduction qualification these days. It's essentially spelling out something that doesn't change anything whatsoever about how you would address or communicate with said person.
You may as well put: [Name] [A-level Grades]
Freefaller's example is a different matter though when you're working within an industry that actually distinguishes people based on their qualifications.
I don't think there is anything wrong with distinguishing yourself through your qualification.
Dr Tummy for example
