SSL is a very server-intensive process and will affect the performance of your web site. Any time you are conducting a transaction then SSL is suggested. However when your customers are viewing product information SSL mode is not required. If in doubt submit a ticket, ask for a security audit, explain your situation and we will give your site a basic security audit at no charge and let you know what needs to be done.
(Advanced security audits are also available on request and our normal labor rates of $5 per 15 minutes of work apply. Submit a ticket for more details.)