adding an EventListener to an Enter_Frame event function

Question

I was just curious if I add an a EventListener such as addEventListener(MouseEvent.CLICK, onClick); Inside an ENTER_FRAME event function will it add an instance of that MouseEvent Listener every frame? Here is my code now just wondering if this is bad practice:

    addEventListener(Event.ENTER_FRAME, engineLogic);

inside my engineLogic function:

    //Max objects for rock throwers on left 
        if (aXPositionArray.length == 0)
        {
            //Remove listener to add more and make button turn grey etc
            rockThrowerSpawnScreen.left.removeEventListener(MouseEvent.CLICK, chooseSpawnSideRockThrowers);
            rockThrowerSpawnScreen.left.visible = false;
        }else
        if (aXPositionArray.length != 0)
        {
            rockThrowerSpawnScreen.left.addEventListener(MouseEvent.CLICK, chooseSpawnSideRockThrowers);
            rockThrowerSpawnScreen.left.visible = true;
            trace("LISTENER");
        }

or does it only add it once and checks the function every frame?