Pretty much worthless for uncharted hazards.
Does remind me of a cruise ship which ran aground off Nantucket a few years ago on a clear moonlit summer evening. Apparently the crew put the ship on auto-pilot and were watching television. The GPS cable somehow became disengaged from the piloting gear and the ship ran aground harmlessly about a mile off Nantucket. The local Boston TV stations sent camera crews over by boat. The Greek Captain said, more or less that it wasn't his fault, he was watching TV and the instrument failed. The Boston Chief of Harbor, a Coast Captain, asked to comment, said aids to navigation don't relieve a crew of responsibility. He remarked disgustedly, you can look out a window.
Within 24 hours a Coast Guard party boarded with an American "prize crew" and all the officers were taken off as guest of the Coast Guard for a couple of days and the ship brought in to Boston. All the ships officers had their U.S. tickets lifted within 72 hours and the owner was told he would have to replace them before he could have his boat back.
It was pure luck no one was killed.