How do I scale a Mobject using a Manim updater?

Question

1. I can scale a Square mobject as follows with self.play()/Scene.play():

   square = Square(fill_color=RED, fill_opacity=1)
   
   self.play(square.animate.scale(3))
   self.wait(3)
   

   

2. But I cannot achieve the scale behaviour as above using this simple add_updater method. All I get is a blank screen:

   square = Square(fill_color=RED, fill_opacity=1)
   
   def scale_up(mob, dt):
       mob.scale(2*dt)
   
   square.add_updater(scale_up)
   self.add(square)
   self.wait(3)
   

Questions

1. How can I achieve the behaviour of No 1 above with add_updater, or other updater techniques?

2. I know that I can successfully animate an item with updater methods - such as doing mobject.shift() - even without using self.play()/Scene.play(). Can the behaviour of No. 1 above be achieved without using the Scene.play() method?

3. It appears that you can .scale() an object with scene updaters, instead of Mobject updaters. Why?