Why Do Certain Major Leaguers Practice Bunting?

I stumbled upon this image of Adam Dunn practicing bunting during spring training and immediately thought to myself, well thats a complete waste of time. In what situation would you actually want your power hitter or one of your best hitters to sacrifice bunt? How many times has Adam Dunn actually bunted in his career? Perhaps practicing making contact and boosting his average above .240 would be of better use?So I did a quick google search and found this. With two sacrifice bunts in his career and runners on 1st and second Dusty Baker asked Adam Dunn to bunt. He failed twice and was forced to swing away. He returned Dusty's confidence in him by.... blasting a 440+ foot walk off home run.I'm not anti-small ball by any manner, but why have a massive power hitter that you're never going to ask to bunt even practice it. It's just a waste of time.