Zero Loss means that as soon as you start moving the shift paddle the cable starts moving, no play at all. The orignal Force and Rival shifters had a long throw on the front shifter that could be a pain to shift, especially if you have small hands. It was also more difficult to get set up correctly. The zero loss is supposed to be a big improvement there. I haven't ever used a Red shifter, but I don't have any issues with my rival rear shifting so I don't know how much it is an improvement there.