you don't "need" it but i would recommend it, it makes the depot dissipate much better, less knots and makes the oil thinner and easier to filter and inject
3ba, 7-10bb is what i use
so if you want to make 4 10cc bottles which is 10 grams at 250mg/ml you will need 1.2ml ba and 2.8bb if you go 3/7 along with 28.5ml of sterile oil