For Your Safety.
Paying attention to your tree's distance from power lines can help prevent nearby power lines from being knocked over by a tree or large branch, as sometimes happens during storms. If anyone touches a downed power line that is still energized, the result can be serious injury, even death.
In addition, because trees are full of sap, they are good conductors of electricity. Children can be electrocuted if they touch a tree limb that is too close to a power line.