You need to keep all of them "fresh" and without seeing them pitch, my guess is they each give a different "look."

Sometimes teams gear up to face gas (Randy Johnson) and if a team starts their pitcher who can locate it well and "spin it" as they like to say (Greg Maddox) that team's approach is out the window and the probably get mowed down. Or if a pitcher is a drop ball pitcher, so all the hitters eyes have been focusing down and then you bring in a rise ball pitcher their eyes have switch up in the middle of a game and/or inning and it throws you off where your eye focus has been the previous 3 or 4 innings.

Once again this is without seeing us pitch this year.