A butt connector is a small aluminum tube with a plastic cover, whenever you crimp the butt connector onto the wire the metal of the butt connector itself conducts the electricity or whatever current you have ... the dielectric grease is non-conductive and only helps the connection to avoid moisture and corrosion. We use dielectric grease on each and every electrical connection on our airplanes and I've made it a habit to use it almost any time I'm doing any type of electrical connection around the house.
What Is Dielectric Grease? 
