When done properly, pruning can enhance a trees beauty, reduce chances of root or branch failure, and prolong the useful life of trees. But when done improperly can result in just the opposite results.
Objectives of pruning. The main objectives of pruning is to create strong structure, produce a healthy and pleasing form, with removing the smallest amount of living tissue as possible.
Evaluate the tree before pruning. What is the functions of this tree? Will pruning enhance those functions? Ask why am I pruning. Is it because of dead branches, broken branches, branches that are too low for my mower, or does it just seems to be the right thing to do at the time? You should always have a good reason for pruning. During the active growing months leaves are the food factory for the tree, without them a tree could not excise, and with too few a tree will soon decline.
A tree that requires several prunings annually to maintain a desired size should not be considered for pruning, but for replacement. If your desires are for a smaller tree why not replace with a smaller species? The true beauty of a tree is one that is allowed to grows to it's full potential.
A high Maintenance tree is one that has been abused by improper pruning.
Tree topping (tip pruning, rounding over, heading back) involves cutting large and small branches back to stubs and is not a recommended method of pruning. Not only does topping a tree increase branch failure, it's result is a disfigured tree. Just because utility tree contractors and most residential tree companies continues topping doesn't make it right. Tree topping should be avoided.
Over-thinning is when excessive inner foliage of a tree is stripped out. This encourage the tree to grow very long branches without proper taper. Not only does Over-thinning increases branch breakage, and promotes sprouts, it's result is a disfigured tree. Over-thinning should be avoided.
When in doubt get other opinions, the internet is a great source for info.
Looking for a certified arborist in your area? Check certified arborist list at International Society Of Arboriculture.