the pump pumps continuously and the carbs have floats in them that cut the incoming fuel when they reach the top (bit like the ball cock valve thingy in your loo) when the carbs are full and dont need any more fuel the pump just dead heads (pumps nowhere but its only low pressure)however when the cars running you dont get that situation because there is a constant small use of fuel and therefore a constant small replenishment, the reason that its recomended that you connect up to the oil pressure switch is because if (god forbid) you had an accident and the fuel lines split and you where unable to turn the pump off, the fact that the engine would stall and therefore have no oil pressure and therefore cut the pump out and stop it pumping fuel everywhere. basicly its a safety feature and its your choice personally i would do it. is that all clear? if not ill try harder next time