It's two different things... Hcg doesn't spark NATURAL testosterone production. It keeps your balls working and keeps them from shrinking but is doing this artificially to put it simply. It is actually suppressive to your natural testosterone production. PCT is not.
Why you should use HCG ON cycle:
We know that steroids shut down production of LH at the pituitary. This means you no longer produce natural testosterone because there's nothing to stimulate your Leydig Cells in the testes. The reason your testicals normally look "full", is because they're loaded with testosterone. When your natural testosterone production is suppressed, your testes atrophy (shrink), because they're empty. Make sense?
Injecting HCG results in a "mimicked" LH. So although your pituitary gland is not secreting LH, your leydig cells, in the presence of HCG, are stimulated by the mimicked LH and begin to produce testosterone. So there's your solution for preventing testicular atrophy while on cycle. But there's more to HCG than just reversing atrophy. Let's have a quick look at some other reasons to use HCG.
Benefits of HCG during your cycle:
1. Prevention of testicular atrophy.
-- This is done by mimicking LH and restarting natural testosterone production in the testes.
2. Speed up recovery.
-- This is done by mimicking LH so that your Leydig cells remain stimulated. More on this in the next segment.
3. Balances hormonal fluctuation. (Mainly TRT patients and dose dependant)
-- By strategically timing hCG injections, you will prevent "dips" in serum levels.
4. HCG in involved in the process of production for DHEA, Cortisol and Pregnenolone.
-- A host of benefits here. These benefits will combat fatigue and stress, betters your mood, has a role in energy, reduced cardiovascular risk, immune stimulation, betters memory, and more.
Leydig Cell Desensitization:
Desensitization basically means unresponsive. Your Leydig cells are stimulated by the LH signal. If they no longer respond to LH, you will not produce testosterone.
There are 2 ways that could potentially desensitize Leydig Cells:
1. Prolonged LH deprivation: When you inject steroids, your LH production is halted at the pituitary, remember? So if you continue in a suppressed state for weeks upon weeks, your Leydig Cells could potentially become unresponsive, or desensitized. It is possible to reverse desensitization of the cells, but that has been proven to be quite a difficult task. So when you use hCG on cycle, the mimicked LH analog will maintain stimulation of Leydig cells so that you don't run the risk of rendering them useless. This level of maintenance will ensure a much healthier and speedy recovery and one of the most important reasons to use hCG on cycle.
2. Over stimulation of Leydig cells: There is no reason to use more than 500 IU of hCG at one time. And certainly not a good idea to run even that dose on a daily basis. You do not have an unlimited-ever-flowing-supply of Leydig cells. There is only so much stimulation hCG can do. What happens when you dose hCG really high, is that you're increasing intra-testicular estrogen. So you're thinking that you could use an aromatase inhibitor in that case, right? Nope. AI's are not effective treatment for intra-testicular e2. Furthermore; high doses is a surefire way to desensitize Leydig Cells. So we have a double whammy here. And this is just another reason to use hCG on cycle, and not "blast" hCG post cycle leading up to and/or during PCT.
^ If either of the events above occur, you would become hypogonadal (Low T). This is called dingdong-induced Primary Hypogonadism. You're the dingdong by the way.