basically you want to do single prohormones at first to see how your body responds to it. that way when sides start to come up you know whats giving you sides. also, there are prohormones that are stronger that others. the stronger the ph the stronger the sides in most cases. so whe your first starting out you want to learn how to diet and lift while on phs and not have to worry about sides as well. as your knowledge gains ( that comes with cycles) you can use stronger phs and deal with all that is thrown at you. in most cases that is why this is reccomended.