GREAT question.
Ok, so the only time I ever want to push estrogen down into the low single digits, is in the last few wks of a contest prep. At that point, we want you to be dry-dry and how you feel is secondary. During the rest of a cut cycle, we wanto to keep estrogen moderate, but under control. We don't want it too high when fat loss is the goal. On the other hand, when you are trying to gain weight, estrogen will help you to retain more fluid and estrogen re-sensitizes the androgen receptor.
If you push estrogen too high, you'll have side effects. If you push it too low, you'll sides from that as well. Low E can cause stiff and achey joints as well as low libdo. Also loer estrogen can cause issues with cholesterol.
So try to keep it in the normal range year round and then only for competing, cut it down as low as needed but only for limited times