While everyone might want a Rolls-Royce, not everyone can afford one. That's the difference between demand and effective demand. This target market helps focus your efforts. If your good or service appeals mostly to retirees, you might not want to advertise it on television shows or in magazines aimed at teenagers. If your good or service is oriented toward a specific gender, then your marketing efforts would be wasted in magazines and shows primarily watched by the other gender.
Marketing takes many forms besides advertising.
Businesses will often sponsor events or sporting teams to show community involvement. Similarly, public opinion is a marketing concern, and a company will spend whatever it takes to maintain positive perception by the public. Packaging is a marketing function as well, because in addition to protecting the product, it must be attractive. The packaging is what the customer will see on the shelf, take home and look at until the product is used. Shelf and store placement are also important for sales.