Squat depth…you could spark a lively debate between strongly opinionated lifters on that topic. Lots of research has shown different squat depths results in varying muscle growth responses. Some people always believe in full squat depth (“ass to grass”). Others advocate for half depth under the belief it is easier on the knees…though some long-time powerlifters would argue full squats is better on the knees. Again, people have strong opinions on the topic.
Another study is out comparing squats at full depth (140 degrees of knee flexion) and at half depth (90 degrees of knee flexion). They looked at the effect on muscle volume increases on the quads, hamstrings, glute, and hip adductors.
The results: There was not much different between the two in terms of muscle volume growth for the quads and hamstrings (neither really is a great hamstring builder). The full squat group did see significant growth for the glutes and adductors.
The takeaway: If you are going to do squats to parallel rather than to full depth, you may want to supplement with things like the glute-ham raise or adductor machine to build the glutes and adductors. In either case, you will still need other exercises for to build the hamstrings.
Study: “Effects of squat training with different depths on lower limb muscle volumes,” Eur J Appl Physiol. 2019 Sep;119(9):1933-1942. doi: 10.1007/s00421-019-04181-y. Link: https://pubmed.ncbi.nlm.nih.gov/31230110/