I have to go with Nightjar on this. The skid plate on my 14" NFA round has done 4 seasons in WA and is in no need of replacing in the near future. Same with my 18" NFA round.
I actually put the question to Rohan Johnson of Nugget Finder who explained skid plates are designed to protect the coil from the bumps and bashes that will of cause happen, but it is designed to run as close to the ground as possible but not on the ground.
Yep, in theory having the coil on the deck might place you an inch closer to the nugget, but running it on the deck can introduce noise that can mask those faint signals that could mean a large nugget at depth.
I don't look for obvious signals, you'll hear them anyway. I look for absolutely anything that causes a difference in the threshold and that is repeatable. If I am introducing a difference or a noise into the threshold, then that will negate that inch or so closer to the target because I may not recognize it.
However, once I have located what I think could be a target, yes I'll try and coax every little bit of information out of it and that includes having the coil on the deck.
If you are a scrubber and use Nugget Finder coils, their new range of black HD clip on skid plates may be worth considering.
In the end, each to there own and what works for you.
Cheers,
Steve