I got pulled over for driving with NO tail lights or brake lights. There was an electrical problem with my trailer harness. The lights worked just fine when I left. I thanked the officer for pulling me over because, "I'm not worried about a ticket or something - I'm worried that someone might rear end me and get injured or injure me." We figured out that the flashers worked just fine for it, so he sent me on my way with those on. I always carry spare bulbs, fuses, etc. for the car, and keep a brand new set of trailer lights in case of just such a problem. Turns out that moisture had ruined most of the wiring connections.
But, actually, the last thing in the world I would want is someone bumping into my boat and ruining the lower unit. Plus, suing me because a brake light was out. Oddly enough, during the daytime when I'm making trips with one of my smaller trailers (not the boat trailer), I don't even bother hooking up the lights most of the time. E.g., if I'm just making a quick 20 mile trip to the dump or something.