Hey Susan!
Sell sheets are very important!! In essence, they are the one page sheet that describes the main benefits and features of your product. I call on lots of retail buyers and require that anyone I represent has a very good sell sheet that I can email to buyers to see if they have interest in a product. So, having one is truly important and even if you want to license your product to companies you need a sell sheet to introduce your product to executives at the companies you wish to license to.
Jim