Do they attract lightening so they don't hit the building. Do they make buildings less attractive to lightening?
I have worked in the almond processing business for 15 years. Nuts are in shells that are in hulls. The hulls split at harvest. The nuts are run through beaters to remove the hulls. The nuts with the shells are run through sheer rollers. They are 2 rubber rollers where one rolls faster than the other therby sheering the shells off. There are usually a few of these in a row to allow for different sizes. An air vacuum removes the broken shells. For hard shelled nuts they first go through two steel rollers to crack them.
Lightning strikes occur when there is a very strong charge differential available between the ground and (storm) clouds. The voltage may exceed 600,000 volts which is strong enough to ionize a path from the ground to the cloud. Imagine that the path starts at a point on the ground and seeks the cloud in several steps where each step is like a straight line moving upwards to a point on a sphere surrounding the point. None of the steps are in the exact same direction. This makes a very jaggered path (which is why a bolt of lightning is represented as a jaggered bolt). The path will start at a high point such as a tree or building roof. Ionization will start very easily from any pointy object that concentrates the effect at its tip. After the ionized path is completed from ground to cloud a powerful current of electrons will follow the ionized path to the ground. It is like the arcing in an electric switch that is suddenly opened. The lighting rod atop a barn provides a point to encourage the bolt of lightning to initiate from the lightning arrester which has an adequate (copper) cable to safely guide the bolt into the ground. This prevents the bolt from initiating anywhere else on the roof. And lightning arrester protects a 45 degree cone shaped area below its tip, except that the point will initiate an ionized path more readily than the ridge of the roof (which is a relatively poor conductor and not pointy). The lightning always takes the path of least resistance to ground and the lightning arrester provides a safe path.
