If you require sensitive information to be entered on your web site, such as credit card numbers or personal information, you need to secure it with SSL encryption. It is possible for every piece of data to be seen by others unless it is secured by an SSL certificate.
Your customers won't trust your web site without an SSL certificate. According to Gartner Research, nearly 70 percent of online shoppers have terminated an online order because they did not "trust" the transaction. In those cases, 64 percent indicated that the presence of a trust mark would have encouraged them to continue the transaction. An SSL certificate and a site seal could stop people from abandoning your website and that means more money for you.