The reason some guys take anti e by itself is because estrogen aids the body in storing calories as fat. Cut the e, reduce body fat. It will be a minimal gain, but one to be had. You don't need to worry about ill effects by taking Nolva or similar alone, it won't harm you. And there is some research that lowering e levels will can increase test production. Your body runs about a 13 to 1 test/estro level if i remember correctly. Trick the body into thinking its got less estro, it will increase estro and test production. Gains from that probably can't be noticed.