Well, one of the main functions of the meniscus is to provide a better contact between a rounded bone (the femur) and a flat bone (the tibia). It therefore distributes forces more evenly across the entire joint surface. Here is a good schematic.
Back 75+/- years ago when the meniscus was injured, surgeons would remeove the whole thing and the result was severe arthritis from the loss of force distribution. The hyaline cartilege which lines the bone would get worn away, and the body would lay down more bone to compensate (spurs).
Now they just trim away whatever they have to, keeping as much of the meniscus intact as possible. Depending upon the part removed, it may have a big impact on force distribution, or a small impact.
I personally believe that any type of ballistic movement (like running) puts much more compressive force through the joint(s) than squatting. Front squats and pistols will tend to load your quads more than back squats ... is that good or bad? Well, again it depends. In a knee injury I don't personally see back squats as being more injurious than front squats. In fact, in an ACL-deficient athlete, I prefer to get the posterior chain as strong as possible, and that includes back squats.