Determining whether you need a secure server certificate is really very simple.
You will want a secure server certificate if:
You want your customers to transfer confidential information using any form of your domain name, for example, yourdomain.com or secure.yourdomain.com, etc. Certificates are issued on a per-domain name basis and provide confirmation that the domain being visited is owned by the company listed in the certificate. It is highly recommended that you obtain your own secure server certificate; it is the only way your customers can know that they are doing business with your company.