Casting director/voiceover coach, Cindy Akers demonstrates to one of her students why it's important to be willing to take risks in auditioning vs. "playing it safe."
Directors figure that they can always pull you back if you go too far, but if you hold back, they may figure that you lack imagination or a willingness to fully commit to your choices.
One cautionary note. Going too far or being over the top merely for the sake of showing off how creative you are won't book you jobs either. When you make a strong choice, it still has to be appropriate given the context of the script and the scene taking place.