It's not all or nothing. If you are on HRT, which is typically 200 mg/wk or under (I'm on 200 mg/wk), you will be supressed, not completely shut down. In other words your system will still be working, but not up to full par.
Why do this? Because the system wasn't functioning up to full par in the first place. When you have your blood levels checked and come back low on testosterone, you have two choices, either live with it (and all of the negatives associated with it in terms of physical composition, health and mental acuity), or go on HRT.
It's not a choice I'd make if my test levels were normal. But since they're not, I choose HRT. And since I'm committed to HRT, I might as well come in on the high end of normal -- heh, heh.
As far as nuts, they don't go away. You're not completely shut down because the dose is low enough to only supress, not inhibit completely.