On the other hand, if you're securing Sub-Domains, you can go the Wildcard route. When you're generating your Wildcard SSL Certificate you simply put an asterisk in front of your domain name, so input *.yourdomain.com on the CSR and you can secure an unlimited number of Sub-Domains.
Once again, the side-benefit to this is how much easier it is to manage your certificates. Rather than purchasing individual certificates for each Sub-Domain you're doing it all across one single certificate thus simplifying the administrative process. And unlike Multi-Domain certs, there's no paying for additional SANs. You just use the asterisk in the generation process and you're covered.
Purchase Wildcard Certs