I seriously screwed up my back a few months ago so I had to stay away from lunges and squats. Thankfully now I am able to do them but still cautious (don't want to go through that again!) but I only go about halfway down.
If you actually want to practice form and control below parallel is key. But ATG is ridiculous. It can cause injuries and if you are serious about lifting you should learn to utilize your quads, glutes, and hamstrings. And in my opinion ATG depth doesn't do this properly.