Back to the original topic, the reason for the shuttling back and forth is because the Brewers have a number of young SPs who are talented but either haven't built up their innings yet or are coming off of injuries and still building back up and they are trying to manage the workload.
Compounding that is the injuries to Priester and Woodruff who, if healthy, would make the shuttling of Gasser/Crow/Henderson much easier to manage.