I'm guessing for better aero or to duplicate position from your drop bar bike? I was planning to put bullhorns in place of my flat bars, until I realized that bar ends, on the ends, is a lot more comfortable at 58 cm width than 40 cm width on the bullhorns, at least for my shoulder width. Plus, due to more leverage, my hands don't need to pull and grip as hard during climbs. Less aero, true, but I'm all about comfort, and I have clip-on aeros for aero, though I want to raise them about 75mm for comfort.