I only ever close the sea cocks to work them occasionally to stop them seizing. The rest of the time they're open. If they're going to break, they'll do it when underway, when they'll be open anyway. Only other risk is electrolysis, so I keep an eye on that, although recently found a couple of sea cocks I didn't even know I had for the cockpit drains.

Insurance companies say they have very few claims relating to flooding due to sea cocks being left open, but plenty of engine seizures due to them being left closed.