Pruning and trimming are used interchangeably but they do have different meanings. Trimming is more meant to improve the appearance and structure of your tree or shrub. Pruning is more along the lines of removing heavy or dangling branches due to safety concerns. Commonly referred to as crown reduction, this deals with removing branches from the sides or tops of the tree to prevent them from going above utility lines or damaging roofs.
Tree trimming, when done correctly by a trained professional, will lead to better looking and healthier trees in the long-run. If you want the best for your trees we advice going with a professional tree service. You never know when a branch is truly just hanging on by a thread and as soon as you touch it, it goes to fall on you. Pruning professionals are well trained in how to identify and remove such branches, eliminating risk and speeing up the work.