Clojure Agent question - using send-off

Question

I have a couple of questions about the following code:

(import 
 '(java.awt Color Graphics Dimension)
 '(java.awt.image BufferedImage)
 '(javax.swing JPanel JFrame))

(def width 900)
(def height 600) 

(defn render
 [g]
 (let [img (new BufferedImage width height 
                 (. BufferedImage TYPE_INT_ARGB))
       bg (. img (getGraphics))]
   (doto bg
      (.setColor (. Color white))
      (.fillRect 0 0 (. img (getWidth)) (. img (getHeight)))
      (.setColor (. Color red))
      (.drawOval 200 200 (rand-int 100) (rand-int 50)))
   (. g (drawImage img 0 0 nil))
   (. bg (dispose))
   ))

(def panel (doto (proxy [JPanel] []
                        (paint [g] (render g)))
             (.setPreferredSize (new Dimension 
                                     width 
                                     height))))

(def frame (doto (new JFrame) (.add panel) .pack .show))

(def animator (agent nil))


(defn animation 
  [x]
  (send-off *agent* #'animation)
  (. panel (repaint))
  (. Thread (sleep 100)))

(send-off animator animation)

1. In the animation function - why is #' used before animation in send-off?
2. Why does send-off at the start of animation function work? Shouldn't it just go the start of animation function again and never execute the repaint and sleep methods?

3. Is there any disadvantage, as compared to the original, in writing the animation function as:

   (defn animation 
     [x]
     (. panel (repaint))
     (. Thread (sleep 100))
     (send-off *agent* animation))