Trees can make or break the curb appeal of a house. You can see around town tome beautifully maintained trees and some that have never been trimmed. One of the most important reasons to kee a tree trimmed is to prevent major damage from a late or early snow fall. Broken branched not only make the tree look mis-shaped but they can kill a tree of the branch damage opens up the main trunk.
Also, from a home sales standpoint, a beautiful tree makes a house look much better.
If you are going to buy a tree I recommend going to a nursery. The trees from Home Depot have been problematic, most being unhealthy and not very attractive after a few years.
For tree trimming, it's best to trim the upper branches and any long branches to get a more rounded shape. Be careful who you hire. Spend more for a professional job. I've used Arborscape, Family Tree Serivce, Jose Trevino and Asplundh. I've had bad luck with Fielding Tree Service.