Difference between yield WaitForSeconds and yield new WaitForSeconds

Its really simple, I dont see the difference, though. Because I m kinda new to scripting, I have some basic problems. It would be great if you could help me.. The code is below, if you need it.

function OnMouseDown () {

 if ( animation )
 {
     animation.Play ( aniClip.name );
 }

 else
 {
     parent.animation.Play ( aniClip.name );
 }

 if ( GetComponent ( AudioSource ) )
 {
     yield new WaitForSeconds ( audioDelay );
     audio.Play ();
 }