What happens if I don't install the intermediate certificate?
Failure to properly install our intermediate certificate along with the issued SSL certificate means that the trusted-chain certificate cannot be established. This means that when visitors attempt to access your supposedly secure site, they will be presented with a "Security Alert" that indicates that "The security certificate was issued by a company you have not chosen to trust…" Faced with such a warning, potential customers will most likely take their business elsewhere.
Downloading and installing the intermediate certificate on your Web server immediately fixes this problem. The intermediate certificate can be downloaded by clicking on the link embedded in the email message you'll receive upon certificate issuance. It is also available from the repository.