> When a ship sinks, the outcome is more or less the same whether people are onboard or not: in either case the ship will sink

The more difficult question is when a ship is on the brink of sinking. Then, having people on board can make a difference: the extra weight can make it sink, or actions by those people (pumping, plugging holes, closing doors) can prevent it from sinking.

For the captain, the difficult thing is to figure out whether a ship is destined to sink or not.