Whitepaper is an informational document issued by the creators of a certain token to promote or highlight the features that they want to offer with their token. It is use to promote and inform the potential investors. So it's very important to understand first the Token and how it works before you invest your money. Because not all ICOs are going to be successful, so better to study it first. Of course you don't want your hard-earned money be put on something and might be gone in just like that. So be cautious.