I stat there because it’s the lowest note I can play that actually sounds like a good, full note. I don’t think you can greatly increase your range in this exercise and that’s not what I try to do. I use it as a way to warm up the necessary playing muscles which means your embouchure and air support. These are the two most important things for making a good sax sound. That’s the real value of it. Of course as you get better at it and your range happens to increase all the better, and it means you are doing it right.
Yes you should incorporate this to your sax playing, focusing on your air and embouchure, and another thing you might forget about that comes into play is your throat opening. This doesn’t come naturally for anyone but try experimenting with how open or wide you can make your throat because a closed throat can makes the tone smaller.