PCT REVIVES YOUR TESTICLES. With out it, they will wither, die and turn into a poof of dust. All you'll be left with is a bag of sand between your legs.
Just kidding. I'll try to help clarify for you. Ok, so you've got natural test boosters. Note there are overlaps in the ingredients. There are 100 test boosters out there and many have a similar ingredient list, but none are identical. Some work different than others, and as a result are used in different phases of the cycle, ie During and PCT. Running a test booster while on, prevents a complete shutdown(theoretically). Running one in PCT helps bring them back to full working order (theoretically).
Now, you've got your PCT... depending on your cycle you lay one out. Milder shorter cycles need less of a PCT treatment. Longer more intense cycles require more. A lot of guys either run, or suggest a more intense PCT than actually may be needed. But guess what, BETTER SAFE THAN SORRY. That's why a doctor prescribes more antibiotics than is needed to make SURE to eradicate the infection. If you don't correct your body back to homeostasis you'll just lose everything and it will all be a total waste, so, why not spend a little more to make sure that doesn't happen.
Sdrol's are pretty intense. Its up to you to decide what you need, because its your money and your body.
If your still not sure, just search this site for PCT protocols for a beast cycle. You'll find plenty.