"Dielectric grease is a non-conductive, silicone grease designed to seal out moisture and, therefore, prevent corrosion on electrical connectors. Being non-conductive, it does not enhance the flow of electrical current. This property makes it an ideal lubricant and sealant for the rubber portions of electrical connectors".
Therefore, you put all your connectors together before applying a light coat of di-grease around them, otherwise you end up with "weak" electrical connections.