I think this is covered in the FAQ. The B&P are not part of the Master-Cleanse but a lot of people here do them along with something else (i think a parasite cleanse) and call it the "Ultimate Cleanse."
I personally don't do the B&P shakes because (1) I don't believe they really do anything that eating right won't accomplish and (2) I think they detract from the Master-Cleanse where you are trying to give your digestive system a rest. This is just my opinion, and you will hear diametric opposition from my opinion, but keep in mind none of us are doctors here so you have to make up your own mind about certain things.