I think you're misunderstanding estrogens role in growth. You want to have estrogen in your of course, but too much of it can be a big problem, too little can also be a big problem as well. Too much of it can cause all kinds of problems from sexual function, sex drive, gyno mood swings etc, too little can cause things such as joint pain and can limit growth to an extent. AI's control the excess estrogen being aromatized keeping it in check and not allowing it to go too high. Some people use them too much and actually go overboard with them, the trick is finding out what works for you and not letting it get too high or too low. Personally I'd never not run an AI on cycle, all of my cycles include Aromasin or Adex.