In Virginia, the common law has long held that if a neighbor's tree encroaches on your yard you may cut the branches as they cross the property line, but any damage the tree does to your property is your problem. Your neighbor can even sue if your pruning kills the tree. In 2007, the Virginia Supreme Court overruled this 70 year-old precedent, making it your neighbor's duty to prune or cut down the tree if it is a “nuisance.”
Which rule is better: the new rule or the old? What would the Coase Theorem say about the two rules?