the pcv valve allowes the vacume created by the motor to draw presure created by the pistons and rotating assembly out of the crank case with out causing an open vacume leak . it has to go some were ,with out the pcv valve hooked up it goes out the breather cap. and can cause seal failure. but if you are seeing smoke from the breather cap you probably have piston ring blow by /worn rings .
Smoke from the breather is combustion blow-by. Some amount can be expected and this is the purpose of the PCV valve, to create a vacuum in the crankcase to funnel the vapors back into the intake stream to be burned. The PCV valve reduced hydrocarbon emissions by about 95% and was, and has been, the single most effective pollution control ever installed on the automobile engine. The side benefit is that along with combustion blow-by it also removes moisture from the crankcase greatly extending oil life and preventing sludge. You should reconnect the PCV to a manifold vacuum source as soon as possible.