People who carve meat are called butchers. Sometimes people who cut trees earn the same name. There is an art to trimming trees and while an arborist is an extremely knowledgeable and valuable resource not every tree needs an arborist. Arborists are probably best used in the planning, development and maintenance of an expanse of trees.
No branch should be removed without a reason. Trees produce a crown in order to create the sugar they need for growth. Excessive trimming will cause a slower growth and even weaken the tree. That said sometimes trees need to be pruned for safety reasons such as power lines or building being too close. Sometimes they need to be pruned to let air and light penetrate. Dead or diseased limbs should be cut anytime but the sooner the better, and definitely before the spring growth. The best time is as far away from the spring growth as possible. That growth takes all the energy the tree has and it is at its most susceptible to damage just after a growth period. Crowning, taking off the top of a tree can be performed in a number of ways. They can be cleaned thinned raised or reduced. Cleaning involves removing dead or crowded branches, or branches that seem to be slow growing, while thinning is to allow air and light to penetrate all the way to the ground so requires selective cutting to open up the foliage allowing for fuller foliage in the future.
. Raising the crown calls for removing lower branches, while reduction is the opposite effectively lowering the top of the tree while still allowing it to grow sideways.