I never do this and never plan to start doing this. I can understand that people are trying to achieve a certain look to their lighting install but do they understand what they are doing to the tree? Maybe people just don't care but I have seen first hand what a tree looks like (inside) after a screw or nail has been driven into it. I used to do some logging in the winter time and you guys should see what the wood looks like after a nail or barb wire has been attached to a tree for years. The nail or wire will actually stain the wood from the base of the tree all the way up to where the injury is. If the tree is not healthy to begin with a nail can be the "nail in the coffin" for the tree. It also sucks real bad to have a chainsaw come in contact with a nail or wire.