Yes, they place alot more stress on the connective tissues and joints, because the weight is alot more. Look at it this way, John Little and Pete Sisco, the creator of powerfactor, if they say that it is dangerous, and powerfactor is nothing but partials and training infrequently, if someone once recommended doing partials all the time, and now they say it is dangerous, they must know from experience that it is. They probably had alot of trainees with power factor that got injured. So, even though I dont agree with alot of their training methods, take their advice about the partials, because they probably experienced alot of empirical evidence on it.
But, if you still want to do partials, no matter what the injury risk is, I would recommend, do some full range reps, before you do the partials. For example. Take a 5rm weight. Do 4 reps, and to keep the tension still on the muscle, start doing the partial reps. This way you still maintain strength along the entire range of motion.
But if you just want to do partials on the squat with 600lbs, instead of doing full squats with 400. I would get alot more growth stimulus doing the full squats, than I ever would doing the partials with alot more weight. Plus, the injury risk is severely increased with the heavier weight. The only time I think heavy partials are necessary, is when you have to psychologically get over a weight, and you use a heavier weight than normal to make it seem light. Also they are used to overload a particular muscle in a compound movement. Like rack deads, to overload the back. Rack benches, to overload the triceps.
Anyways, good luck, and hope you stay injury free.