Hm... what if you go wider? Maybe you'd squat full better. If I were to keep a shoulder width stance I'd have a very hard time full squatting (where full = below parallel for me).
And I think another thing that needs to be emphasized is to never twist when the back is loaded. The discs themselves are pretty sturdy when loaded "liniarly" but they are not built to sustain twisting under load. So don't do twisted crunches or twisting (even your head to see if you put the bar correctly onto the pins etc) under a loaded back.
At least this is what I know about the spine and the discs.
I'm afraid of doing loaded calf raises. One - that my legs would slipp and a mess would happen and two - I've always had back problems after doing them. So I do them on one leg and use dumbbells/plates in that leg's corresponding hand. Going for 15-20 reps.