Secure Sockets Layer, are cryptographic protocols designed to provide communications security over a computer network. Several versions of the protocols find widespread use in applications such as web browsing, email, instant messaging, and voice over IP.
Having an SSL on your site enhance the security of your data.
There are many bloggers, website owners, enterprise or startups who ignore the importance of SSL certificate.
However, if your website is not installed with SSL, all the communications sent and received from your web server to customer is not encrypted. It is really simple for invaders to attack these kind of unsafe communications.