PRO: If you convert products to Test Prop or Tren Acetate then you are 100% guaranteed the product you are making is legitimate.
CON: If you are converting powders you buy from various sources you have no idea what they are and could be the same shit some guy dumped in toothpaste from China and kill yourself, LOL.
PRO: you control the quantities of BA/BB and what kind of oil goes into the product, the processing, filtration and if you heat, the heating
CON: you control the quantities of BA/BB and what kind of oil goes into the product, the processing, filtration and if you heat, the heating
oh wait, said the same thing twice

...I think you can see how if you are careless you could make non-sterile product though but if you are careful then you make a perfect product.
Opinion: if Test Prop and Tren Ace are what you like and those two elements are ALL you like then homebrewing is the best thing you can do. MOST will disagree and say they have never had a problem from their sources in getting the right powder...i prefer to stay away from powder from sources because I truly don't know what's in them.