My bike lives outdoors, under a cover. I thought that a little grease might save me some headaches later on down the road. I did plug and coil wires last year and thought that fuses might be a good application too. I replaced the headlight bulb in my car the other day. I see Honda must have put grease on the bulb base at manufacture time. Its still in there doing its job 13 years later, and not too dirty. I will step out on a limb here and say my Sportster fuse box is cleaner than the headlamp assembly on my car.
Dielectric grease will prevent corrosion. Take your pick, corrosion or a little dirt. My current bike has 118,000 miles on it and haven't seen any bad effects from the dielectric grease yet. Nor did I ever on previous bikes.
Dielectric grease is also great under the rubber boots on your cable adjusters. Makes them slide when you need them to, and cuts down on corrosion to boot. Just a VERY thin film is all you need. Won't trash the rubber, either.