From Masnsports.com Roch Kubatko:
"We wanted Brian to get the feel for his changeup back and start," Showalter said. "If we had an injury or some trade had happened or something, Brian... Because nobody had a better spring than him with the exception of maybe Zach (Britton). So, with Troy being out, we wanted to make sure that we had a feel for the left-handed part of that, especially with four right-handed starters. And making sure you have length."
Obviously the changeup was a huge point of emphasis over the winter.