Answers are all I appreciated, every one of them, great information.
Keeping Up, your example is actually very helpful or maybe enlightening is the better word. Sounds like most issues are related to Shore power and/or being in Marina with Shore mains. Am I correct in thinking that someone CC'ing would have less risk of sudden serious damage? Of course I realize that anything is possible.
Our goal, which being a few years off will may change, is buying a boat that is is good shape. Full survey will be done or I won't buy. Expecting to spend a few weeks in a marina, fitting it out to suit us. After that the goal is just CC the system. Depending on winter weather we might moor up for 2-3 months in a Marina? We are thinking we would like to do this for a couple of year and then sell the boat and move on to some new adventure.