I've recently switched my routine to incorporate more machines.. Although I'm in it for the long haul, so to avoid injury I keep the big compound movements as the core of my routine.
Yeah, think about your elbow. There's no where for it to go, you've got your arm and the weight in your hand pushing down. Leaving much less opportunity for movement other than the desired. And of coarse you could mimic the same perfect form with free weights but it would require many other muscles, taking attention away from the agonist.
IMO, I think machines have a place in every BBr's routine. And they can play a role in a PLr but not nearly as much or as often, usually helping with injuries and weak points.