If you cut a branch in the wrong place the wound will start to bud and send out a lot of weak growth. It is a reaction to a perceived problem in the tree, such as a disease or damage. The plant wants to produce more seeds to offset its impending doom. With fruit trees you want that type of growth so that you get lots of buds, flowers and subsequent fruit. A hardwood shade tree is a different situation. Same with a rose bush, berries, etc.