I do not see a single good reason for us to still rely on the antiquated mailing address system in the 21st century. Aside from the hassle of updating your address every time you move and the high probability that not every system of record always gets updated, I think it is obvious the risk of letting complete strangers know your physical location when all they need to do is mail a letter.
I propose a new system where everyone is assigned a unique "mail code" that maps to a physical location/address. This code would never change sans extraneous circumstances. The government/USPS would maintain the mapping between the code and physical address, and a website would let people quickly and effortlessly update their physical mailing address. Think of it as e-mail for snail mail.