Here they used to trim them, and the contractors they used to hire kept cutting through lines and having accidents.
I knew someone's husband that was one of them, he slipped and cut through a main line causing a ton of damage...seriously would have never let the guy run my weedeater. I think he was finally laid off 2 years later when he rolled their truck.
Now they only come out and trim something if it's definately causing a problem by hanging on the line, no more preventive maintenence...and then they only trim the branches that are posing a problem.