From what I know about it, it doesn't hurt natural test production, so I use it during PST when endogenous test production is low. I have always used it in PST and have found that I don't tend to lose much after a cycle and don't develop gyno.
I have also used it during a cycle since it helps mildly with the some of the sides (not as good as nolva). My logic here was that at least I would be getting some bang from taking it. However, I don't really plan on doing that in the future; I will just take more Test and talk nolva eod. It will cost about the same, but this should be more effective at increasing gains and reducing sides.