Rehab is for quitters. But seriously, the infinite scalability of CrossFit makes it the ultimate in rehab as well as in elite physical preparation. Granted, many in the main stream/bodybuilding "fitness" communities will tell you there are appropriate times and ways to use machines, but I will tell you what I tell these people. There's a better way. For instance, one of my buddies insisted that when training for pull-ups in the marine corps it was better for him to do lat pull downs because he could do drop sets and thus do more reps. This is crap. He would have been better off to grease the groove, learn how to kip, do jumping pull-ups when he got tired, etc. Anyway, though some machines are better than others, there is always a better way, and thus, if your goal is the best level of fitness possible, then I don't see how you could ever justify using machines.