Understanding about how our body clock works may allow us to adjust it. This would be a boon not just for shift workers but for the thousands of people who suffer from Delayed Phase Disorder (the body clock being mis-set to a period of longer than 24 hours) or its reverse. It might offer the possibility of a cure for jet lag, even.
And its an important thing to think about for science fiction writers too. A day on Mars is 24 hours, 39 minutes and 35 seconds long. It is just about possible for a trained human to adapt to a day that length, but what about any animals a colony might take with them? And once we get into extrasolar planets, we might be dealing with 20 hour days or 30 or...who knows.
As far as I know nobody in a story has thought of using some kind of therapy to adjust a colonist's body clock to a different length of day...I'll have to remember that for the future.