I just never felt they did anything for me... strength gains never correlated to a heavier squat, I think the injury prevention is overblown, as well as the muscle imbalances between the legs. I think it can be useful for those who do have muscle imbalances, i.e., can't activate certain smaller muscles in the leg when they do a squat, but I feel I can squat using my quads, adductors, glutes, and hams just fine. So I put my focus to more squats, zero lunges.
Also I forgot to answer your question about how to program the squats. There is multiple ways of going about this, but if you really want a big squat for better performance, do the squat often, like 3x a week. What I've been doing is this:
Front squat, 70% x 3 reps x 10 sets
Back squat, 70% x 3 reps x 3 sets
Back squat, 70% x 3 reps x 10 sets
Front squat, 70% x 3 reps x 3 sets
Back squat - heavy single, or max if you are feeling good.
-- And then every week for Tues/Thurs, do 75%, then next week, 80%. And alternate maxing out on Front or Back Squats every week. This should get you a bigger squat very fast.