A wise friend of mine once said that if you are a good enough actor to play every moment perfectly, no one will be able to tell that you are a good actor. You have to be able to have some moments where your acting does not work so people can see the moments when you are really doing a great job. It is for this reason that he always chooses to play some beats and moments in his performances poorly, so that when it really matters he can nail the character and really give an effective and affecting performance for the audience.
This is one reason why I enjoy clowning as a performance style. It gives you a wide range of emotions and expressions to play. If you play the majority of any piece at 120% silliness and then suddenly shift gears and become very small - or better yet pull out a gun and shoot the main character - the audience is forced to sit up in their seats and take notice. Controlling the size of the performance is much like the screen director's ability to control the camera angle; it helps point the audience toward what they should be looking and and what you, as the director, want them to focus on.