It's true that MLB managers have the least impact on wins/losses of any major sport. But you only need to look at the Twins division to see that it matters on the margins. Terry Francona is terrific and his teams always win more games than they should. If him and Rocco switch jobs, the Twins are 5 games up on Cleveland, IMO. If he and La Russa switch jobs, they White Sox might be 8-10 games up on both.