Raising removes the lowest branches to improve clearance for pedestrians, structures, and vehicles or in certain cases to improve the view. A large portion of our work involves pruning to create the necessary clearance for homes (oftentimes roof clearance). Obviously at bare minimum we want to keep trees from contacting houses but beyond that I feel that an envelope of space around one’s house is beneficial to keep air moving in order to reduce mildew and maintenance costs.
The key here is to balance adequate clearance with being kind to your trees. Remember good pruning isn’t once and done, it should be revisited every certain number of years depending on your specific circumstances.