This time is time not used for other activities. It is almost impossible to think of an activity that requires less involvement of the participant than watching television. Almost all other activities that are considered pleasurable require some sort of input from the participant. Playing a game of basketball teaches a person to interact with others and teaches some degree of problem solving. The child who plays with dolls learns something about how people are supposed to interact and develops a potent imagination.
Television restricts such benefits due to several factors.
First, the act of watching television doesn't require a mental image to be conceived and the viewer thus fails to develop a mind that can easily visualize spatial relationships. For many creative tasks, including the fine arts, this ability is of critical importance. Secondly, the content of television is broadcast to a massive audience. Since a great number of people view the same material, television programs often present similar ideas to a great number of people. This hinders creativity because it often leads people to act as a mosaic of traits they learned through television rather than through personal experience.