Every good forum needs a whipping boy, so I am about to volunteer.
I use the Leg Press and the Hack Squat machine in my gym!!!
When I finally got back into the gym the first of the year, my back would spasm doing a bar only over head press. I could do a few reps of back squat with only the bar. I started using the hack squat machine and the leg press to work my legs. After a few months of concerted effort, I got to the point I could do back squats. I could not bring myself to trust my back above 165#'s.
With my Current program, I do Hack Squats on Monday - 20 rep back squats on Wednesday and Leg Presses on Friday.
On Tuesday and Thursday I do Farmers Walk!
"Today is always the perfect day to train"