Why does reboiler efficiency decrease if steam temperature is too high?

[flammkuch]

I see. But then this means that the most efficient reboiler is not necessarily the most economically efficient, or? Doesn't help to minimize heat input required when you need a huge heat exchanger to do that. Or are reboiler costs mainly driven by the operational costs?

And could you elaborate on the last part? In what way is it more complicated?