The Power Rack is always cool for
Pin Pulls (Partial Deadlifts)
Rack Lockouts (Partial Bench Press)
Benching without a spotter
Incline Benching without a spotter
The Smith Machine is for
Extreme Stretching (DC Style)
I’m not saying smith machines are the devil. I’m just saying if there’s someone whose got a power belt and is sitting on the bench next to the power rack you’re doing inverted rows on, you should probably just do them at the smith machine.
Curling in a Power Rack or a Squat Rack is not to be done unless there is another Power Rack available. If your gym only has 1 squat rack and 1 power rack, then curl in the squat rack so you do not prevent anyone from doing Pin Pulls or anything else that demands the safety pins be adjusted. If your gym has 2 open power racks, you may curl in one of them.
If you are curling in a power rack or squat rack, you must have already done an exercise more badass than curls that day. So if you’re doing an Upper Body day, save the curls to the end. If you’re doing a full-body day, save the curls for the end. If you’re doing an Arms day, you should have done Close Grip Bench Press before you started curling.
If you are doing ultra cheat-like-hell curls to improve your discus throw, you should go use the bumper plates or a Strongman Log.