From bodybuilding.com:
So we now see, contrary to the dominating opinion of the times, that anti-estrogens alone will do little to raise testosterone levels in the early weeks of the post-cycle window. This leaves us to focus on a very different level of the HPTA in order to hasten recovery: the testes. For this we will need the injectable drug HCG. If you are not familiar with it, HCG, or Human Chorionic Gonadotropin, is a prescription fertility agent that mimics the bodies own natural LH.
Although the testes are equally desensitized to this drug as LH (they both work through the same mechanism), we are administering it as a measured drug and are therefore not constrained by the limits of our own LH production. We similarly can use HCG to provide a bolus dose of LH (of our choosing), which works only to augment the recovering LH levels we already have in the body. In essence we are looking to shock them with an overwhelmingly high level of LH activity, coming from both endogenous and exogenous sources.
We want it to reach a level far above what our body, even when supported by anti-estrogens, could possibly do on its own. The result can be a rapid restoration of original testicular mass and functioning, which would allow normal levels of testosterone to be output much sooner than without such an ancillary program. What we are looking at now is HCG actually being the pivotal post-cycle drug, while anti-estrogens are relegated to a supportive role at best.
So why not use HCG in all post cycle therapies followed by clomid/nolva.