Some of these favorable times are when you are training around an injury, doing post -rehab work after an injury, when you don't have a spotter or trainer present and you want to use heavy weight and when free weights are not available. I have been healing up my shoulder after a labrum / rotator cuff strain that I got from doing a one arm dumbbell push press with a 95lb dumbbell.
So instead of stopping my training while waiting for my shoulder to heal, I decided to use mostly hammer strength weight machines with the heaviest weight I could move. This allows my shoulder to heal and keeps me from losing lean body mass and strength. But to make it worth using the hammer strength machines, I set a standard for myself to try to use no less than four 45lb plates on each side and when possible to use five 45lb plates on each side.
Today, I did a chest and back workout using the hammer strength chest press and seated row machines. I used four 45lbs plates on each side for both exercises and I did about 6-8 sets of 3-6 reps. I even managed to do some heavy single rep sets on the chest press machine with five 45lb plates on each side. It was heavy as hell and I still managed to get a full central nervous system stimulus that broke me off at the grass roots. The beauty of it was that my shoulder didn't hurt at all and I got in a great workout.
Check out the pics below. 4 and 5 plates is heavy to me no matter what I am doing.
So don't be afraid to train around an injury. Use the tools available to you and do what you can. Then when you heal up get back to the basics with bodyweight, barbells, dumbbells and kettlebells. And as always, follow the mantra: "Go Heavy or Go Home".