I never had to think about this with the MacGregor. Now that I have a larger boat with an inboard, fresh water system, AC\heat, it's a question. Is there a risk to leaving shutoff valves open in the slip? If a thru hull leaks, a valve isn't going to matter. Isn't it better to leave them open so systems don't overheat and drains drain? Where's the logic in closing them when you pack up and leave? What am I missing?