Trees need to be pruned to protect against falling branches. If the trees have grown so tall that they are closes to overhead power lines, DO NOT be tempted to prune them. Call your service provider to do the job. Thinning out the crown of the tree allows more light and air flow. Remove all diseased branches and dead ones. To encourage height remove all the lower branches. Stand back and look at the shape of the tree and decide if there are any other unsightly branches that need to be removed. It's best to prune in winter, especially with deciduous trees as one can see the branches more easily. Pruning also stimulates fruit and flower yields. There is controversy regarding the use of a tree sealant after pruning and it appears that the sealant does not reduce decay or disease.