With very few exceptions, especially in the consumer space, you won't need advertising if you actually need something. You'll search it out or your friends will tell you what to buy.
Advertising serves as a way for the capitalist class to exert veto power over other aspects of society by yanking funding at opportune moments (see the current Google snafu or Bill O'Reilly's departure from FOX (which was an example of this power being used for good indirectly via public pressure)). It also allows for shows of dominance, strength, and to move fucking product by creating an awareness moat vs your competitors. This means that people often already know they want to buy something, but they'll pick you instead of the other one which is fundamentally different from advertising performing a public service.