When our starting pitchers return after the All-Star break, we will have more promising arms than we have room for them. As most of them are battling injuries, it may make sense to switch to a Six-Man rotation. While Cahill and Gonzalez may not need the extra rest, the rest of staff can certainly use it. It's not like we're in a pennant race and can't afford to take a start away from Cahill to give to Ross. A six helps build up the value of our number 6 pitcher, and makes it more likely we can trade him for a bat if the opportunity presents itself. While this was once a radical idea, The Chicago White Sox and Kansas City Royals have gone to six-man rotations this year and had success. We would do well to consider doing the same.
[Edit] Hat tip to PDXAthleticsfan for pointing out Cahill's ERA is much better on 5 days of rest, as he is less prone to give up home runs. Since last year his record is:
4 days rest: 122.2 IP, 47 ER, 76:42 K:BB, 14 HR, 3.45 ERA
5 days rest: 64 IP, 12 ER, 35:17 K:BB, 2 HR, 1.69 ERA