The philosophy of zone defence is that every player is responsible for an area of the court rather than a particular opponent. Players take up positions on the court in various formations and each moves according to the movement of the ball.
The zone defence is easy to teach which is probably why many junior teams prefer the zone. However I cannot overemphasise the importance of learning the fundamentals of man to man defence. A zone defence tends to weaken individual responsibility. Defensive stance tends to become more erect and it is rare an aggressive active, hustling attitude is maintained.