I've always had enough of a gap to fit a strap between the deck and the hull. On my launch though, I had to kind of do the hooks upside down with the main hook part around the top half of the stern eye, and then the backside of the hook pulled down on the bottom half of the stern eye...kind of hard to explain but it worked great. If I just hooked it like normal the hooks pulled down on the platform, not the hull.
I always strap my boat, Michigan roads suck. Will a boat bounce off? No. But I don't like the hull having the opportunity to bounce up and down on the bunks, I'd rather have the trailer axle and tires taking the load.
I usually back my boat in with the lights hooked up because of the surge brake; they are waterproof so I don't think it's an issue. I'll often unhook them though just in case once it's in the water. If you have a leak and water is getting in, it's going to get in no matter if you unplug your lights or not and eventually they will blow (I don't have LEDs though so I'm not sure consequences of water getting in those). I've heard it before too, and my dad taught me that with our boat when I was a kid, but I've never had an issue and I've had multiple boats, jetskis, etc over the years. Worst thing that can happen I think, beyond blowing a bulb on the trailer, would be blowing a fuse in your tow vehicle if something shorted out.
2006 Moomba Mobius LSV
replaced 2000 Supra Launch