Here's a good way to look at it.

Q: What's the purpose of PCT?
A: (short answer) to stimulate natural testosterone production.

Conclusion: If you are a TRT patient, meaning you suffer from low testosterone or sub-optimal levels, your body no longer has the ability to produce enough natural testosterone. For this reason, a PCT would be useless for such an individual. It would be like picking up a rock and asking it to turn into a potato.