T Nation

Compounding Pharmacies vs Regular Pharmacies?

I have read a lot but am wondering,

I understand what a compounding pharmacy is, but why would a GP or Endo write prescriptions through one rather than say a CVS pharmacy?

If I am searching for a doc in my area that prescribes testosterone, should I call a pharmacist at a compounding pharmacy, or local large chain pharmacies for docs that are prescribing?