Very useful in my job.
We are restricted to the number of hours we can do in a duty. So, if we have an early flight somewhere, where the passengers, for example, are going to a business meeting/event, they might be there until late in the evening before returning to the airport to fly back.
So we would go to a hotel during the day and have rest there, getting some sleep etc, then go back to the airport to fly the return leg later on. The time we have rested can be used to extend the duty period we can do (up to a certain limit).
Although, the presumptions made above seem a lot more fun to me!