Deep Squats ... For Everyone ?

Depends on the client and the goals. Personally I love to powerlift, so I squat, and I squat low.

I agree with Bryant, in that as long as most trainees progress slowly and have correct form, there should be no knee issues. In fact, if you look at the mechanics of the movement, partial squats have a tendency to create muscle imbalances, as they are quad-dominant. This can result in unequal pressure being placed on the knee ligaments.

That being said, there ARE some people who are going to have mobility issues, particularly those who have no exercise experience or previous injuries. I think squats should be part of a progression and should be worked into, much like Karin has stated, as some clients will not be able to effectively handle their own bodyweight. For some of us, squats come easy, but the squat is actually a fairly complex movement that also requires a great degree of balance and coordination.

Good training is key here, as there are a lot of things you need to pay attention to when you are having a client squat. Generally, I have healthy clients go as low as they can before they lose ability to maintain lumbar curve (this is not the only thing I am looking for, but for the sake of brevity...). My end goal is to have them go low enough so that the hip crease is below the knee, however, there will be some people who simply cannot go this low without a LOT of mobility work...and some can't go that low at all.

As for the leg press, I am not a big fan of the movement, which I believe is, at best, an assistance movement. The positioning puts people in a position where they can handle an unusually high amount of weight, but also can place the back in a compromising position, particularly if the weight is high enough to cause the client to lift his/her hips off of the pad. Not good.

I tend to emphasize the squat, for the functional aspect of it and its ability to improve quality of life.