Um...well, if lighting isn't a good enough reason (Just some harmless humor there.) Your house insurance / local electrical code might be. If your antenna were to take a hit and damage your house, you may not be able to make a claim if the antenna wasn't installed to code. I suppose it would depend on your insurance provider. Also, I have noticed that grounding an antenna reduces background 'hiss'. Grounding would also dissipate any static buildup for your station's electronics thereby reducing the chances of damage from static shocks. hth