In media, as in all business, demographics are used to pinpoint potential audience growth and to spot underperformance. All forms of media are targeted to certain audiences.
For example, Cosmopolitan, Woman's Day and Better Homes & Gardens are magazines that reach the female demographic. But beyond that, they target different types of women.
Media companies constantly tweak their products and the way they are advertised to hit a certain demographic group. The publisher of one of the women's magazines who follows demographic trends may decide her audience is becoming too old to attract the top advertisers. So she will focus on putting younger people on the cover and writing articles for a younger female customer to change the magazine's demographic makeup.
In the magazine world, general interest publications that were designed to appeal to people of all ages and both genders sometimes struggle by trying to attract such a broad audience. Life and Look magazines are two examples.
Demographic information doesn't just matter in the magazine industry. Television shows, radio stations, newspapers and websites are also produced to appeal to certain groups of people.