One of the biggest benefits is that you will expand your customer base. While not everyone who orders from the fundraiser will end up ordering from you again, you likely will see a few of them again. Depending on your product, some peole may not even be familiar with your product and this gives them a chance to try it without the pressure of a home party.
Another benefit is the fact that you will make money, as chances are you are trying to make some money with your direct sales business.
If you are trying to earn different promotions or trips with your company, chances are fundraiser sales will apply to these and get you that much closer to the incentive.