Even though you are cutting off parts of a tree by engaging in tree trimming, the act of trimming your tree is actually good for the plant and can even prolong the life of your tree. There are various reasons why. Help a Young Tree Mature If you have your tree trimmed when it's young, it will mature into a more steady tree. Once you are happy with the shape that the tree has taken, you can then have it trimmed so that it maintains that shape.