Wildcard SSL’s secure your entire website, including the primary domain and all of its subdomains. When you’re running a business, like lilysbikes.com, and you need to secure blog.lilysbikes.com, and shop.lilysbikes.com, a wildcard SSL lets you secure all three, and any other subdomains as your website continues to grow.

First off, there’s no limit to the number of subdomains you can protect. If you have a large business site with many subdomains, all of them are covered under one certificate as long as they are at the same level.  

Additionally, when you have a lot of subdomains, it is significantly cheaper to get a wildcard certificate to cover all of them, instead of multiple individual certificates.

Wildcard Certificates are available as Domain (DV) or Organization/Individual Validated (OV/IV) SSL certificates. Due to the industry requirements behind EV certificates, we are unable to issue a Wildcard EV SSL certificate.
 
You can purchase a Wildcard SSL certificate for 1-year or 2-year terms.

If you are using an SSL certificate to cover multiple subdomains on a Microsoft Exchange server, you will need to purchase a UCC SSL certificate instead of a Wildcard SSL certificate, as Exchange requires that each subdomain is spelled out on the certificate for it to work correctly. This also ensures that older mobile devices will be able to properly connect to your Exchange certificate, as there are older mobile operating systems that are unable to recognize a Wildcard SSL certificate.

No. You cannot use a wildcard domain in a UCC certificate. In this case, you would need to evaluate your needs, as well as the number of subdomains you need to cover to determine which type of SSL certificate would work best for you.