I guess that the defense has the least interest from the players. And training defense is just pure boring. Never the less defense is a very important part in team handball. It is of no use to have an attacking team who is scoring a lot of goals if the defense does not work in the other end and the opponents just walk through. It will be demoralizing for the players if it is too easy for the opponents to score and the goalkeeper will receive a nervous breakdown.

A good defense makes it worth the effort to score in the other end. Further more being able to shift between the different forms of defense makes it difficult for the opponents to have a strategy with their attack, and they must find new ways all the time. That will reduce their chances of scoring and their uncertainty will surely result in losses of the ball.