Pruning is necessary for Bonsai trees to set the form of the extended branches and allow the sunlight into the tree. In general, the tip sprout of the Bonsai tree grows fast, but the under sprouts of the Bonsai tree do not grow fast. For that reason, you cut the tip of the sprout of The Bonsai tree and then the under sprout will grow faster. After that new branches will grow so that the Bonsai tree’s balance will improve. If you don't do pruning like this, the Bonsai tree's shape will be disturbed in the future. And this way of pruning increases the number of new sprouts and they increase the nutrition of the Bonsai tree. This way of pruning also increases nourishment from the sun and ventilation improves. Pruning also helps protect the Bonsai from insects.