Using a celebrity to represent you helps to differentiate your brand from competitors. It also can improve ad recall, making consumers remember your ad and that your brand is connected to their favourite celebrity. Choosing the right celebrity can open up your brand to new markets.
People are attached to their favourite celebrity, and they are generally well-trusted by their fans. If they use your product, it shows their fans that it is a product worth using and builds trust in your brand. Seeing a celebrity attach their name to a product also reassures consumers of the quality of your product.