Ad agencies and product companies often argue that the main purpose of advertising is to inform consumers about available products in a straightforward way. Most consumer ads, however, merely create a mood or tell stories about products without revealing much else. A one-page magazine ad, a giant billboard, or a thirty-second TV spot gives consumers little information about how a product was made, how much it costs, or how it compares with similar brands. In managing space and time constraints, advertising agencies engage in a variety of persuasive techniques.