Utilizing celebrity support will make you stand out in a new or crowded market.
If you are new, then no one knows you exist. You can launch a new product very quickly and take months or even years out of your adoption cycle with the right celebrity support.
If you are in a crowded market, you need to find something that will make you stand out and identify you as different from your competitors.
You don't want price or quality to be your only differentiating factor as your competitors can easily counter this with better pricing or higher quality themselves. You want to have something that no one else has. You guessed it. A celebrity.
Having a celebrity will give you a unique advantage that your competitors won't.