I always unplug my lathes because you just never know what could cause an outage and damage the equipment. In addition to lightning, summer months you could experience brown outs due to high energy demands, winds can cause trees to take out power lines and then there always seems to be someone who drives into a power pole! If your lathe it unplugged, you don't have to worry about any of that stuff and I just found it was a very good habit to get into.