pop off valve

ok, this may be a dumb question. but when do you need a pop off valve? im putting a b&m 144 on my slant six. i bought a kit for a 350 chevy. there was no pop off valve on the manifold for the 350. i have been reading online trying to figure out when you need one. do the smaller superchargers not need one? my buddy is making my adapter plate and was asking me if he needs to put one in, but im not sure. i guess it couldnt hurt right? if the car back fires or theres too much boost for any reason the valve will open... thanks for any help

-aaron-