A few studies have shown that the parallel squat is king for maximizing work and overloading on the muscles . High reps with low to moderate weight gives exercisers the least effective way to overload the lower body muscles. The deep squat can contribute to tight knee joints / kneecap pressure . With this in mind , would you put deep squats in your personal leg workout ?
If properly progressed to, maybe. Progressions? Did that many of the people getting certified skip the part on progressions/regressions? Never have a client attempt an exercise that they haven’t demonstrate competence in performing the exercise at the progression level below that exercise level. EVER!
I don’t think squats past 90 degrees of knee flexion, especially if the knees proceed anterior to the toes, are inappropriate for anyone (both genders) who isn’t a competitive power lifter. The post-patellar pressure generated during knee flexion past 90 degrees, especially under resistance overload, is dramatic, potentially leading to significant articular degeneration over time.
I personally prefer the Goblet squats (w/ kettlebells or sandbags) and the pistols (one legged squats using a weighted plate, kettlebell, dumbbell or sandbag) than the traditional squats with the bar. As for when I train my clients, it depends on their fitness level, flexibility and/or any injuries they might have.