When I hear my clients say "We don't have to advertise. Everyone knows who we are." I feel frustrated. Maybe everyone does know who you are. Maybe they don't. Certainly every person in this country, young and old, knows who the USPS is, so why would they have to advertise at all, never mind invest heavily in advertising?
The answer is that you know about the USPS but you may not know what the USPS can do for you. That is the reason why you want to brand your company and then advertise your brand.