Yes, If your website contains logins or web forms getting personal information from customers or gets credit card information from customers, then you need to purchase an SSL certificate. If you do not secure your site with an SSL, there is a sure chance that the data can be intercepted by others and you lose the credibility of your website visitors.
SSL certificates can also be used on web servers for Internet security and mail servers such as IMAP, POP3, and SMTP for mail collection / sending security.