Carlos Zambrano is going through a dead arm stage, which almost every pitcher goes throughout the year. Some bad like Brett Myers went through, and some not as serious like Marmol went through before the break. Larry and Lou will give guys like Dempster, Harden, and Z some extra days to be fresh for later in the month and hopefully in October.
Carlos, Ryan, and Rich have all recently been struggling with control and their speed on their pitches. With a 5.5 game lead in the Central and important series later in the month against the Brewers, Mets, Stros, and Cards, they need their rotation. This is a good as time as any to give them a rest. They have 3 with Houston and 3 with the Reds in the next 8 days with 2 off days. That should be enough time to give Harden, Z, and Dempster each 2 extra days of rest between starts.
This is a very good move by management considering how heavy we count on those 3, the depth we have in the rotation, rosters expand tomorrow, and the importance of the month of September, it could not have happened at a better time. Expect Marshall, Guzman, Lieber, and some other guys to get starts in Sept., especially if the Cubs get a 8+ game lead in the Central.