What's that got to do with anything?

The comment was about the ability to vary power at all, not doing it efficiently.

Are you going to choose to crash into something because it's wasting fuel to vent part of the steam?

A basic of driving a steam engine is not to waste steam, since steam represents fuel, which in turn represents money. As you say, not having an accident is more important than wasting a bit of fuel (hence safety valves on steam boilers), but in everyday operation wasting fuel is a cardinal sin and something that is to be avoided. At one point I was involved in steam rail preservation, and the old-timers used to mourn the loss of engine driving/firing skills whenever engines sat at the platform with the safety valves blowing.

The ship command structure was a form of information hiding, whereby the commander only worried about the speed, whilst the engineer worried about how to efficiently deliver the requested speed.

> Are you going to choose to crash into something because it's wasting fuel to vent part of the steam?

Under emergency you will vent, but under normal operations where you just want to slow down you care very much about efficiency.

Not just for monetary reasons either (though that's a factor) but because the lumps of coal you're not burning now could save your ass in bad weather and make you reach safety instead of being stranded in the middle of the ocean.

At sea, efficiency gets you back to land.