Domain aliases (parked domains) are domains you own that contain no content. Instead, they point to another domain or subdomain on your account. Aliases help hold a domain you will sell or redirect traffic to another domain.
There are times when managing more than one domain is necessary. In cPanel you can manage multiple domains from a single account. The addon domain links a newly created domain name to a directory in your account and stores its files there.
If you use multiple aliases or parked domains in a cPanel account, you may want to change the primary domain used for the cPanel account containing them. Wanting to change the primary domain in cPanel is desirable for multiple reasons, such as: