Why is depth-of-field important? Partly, it helps solve problems when shooting. For example, if it seems impossible to get a shot in focus, the solutions are: add a light; move back; or zoom out).

The more important reason to understand depth-of-field is to put it to use artistically. For example, in the still at the right, the photographer had many choices. She might have put everything in focus--in which case you would have focused on the whole of the scene: a guy watching football. Or she might have put the game in focus and let the foot and remote go out-of-focus.

Instead, she used depth-of-field skillfully to put the toe in focus, and nothing else. The result: your eye is drawn to the toe... and this becomes a shot "about" the toe. The game and the remote are secondary--thanks to the manipulation of depth-of-field.