Creating a domain as a separate account or subdomain?

I could use some clarification.... For example, we have domain1.com and domain2.com Currently both of these domains are located on our old mail server which will be migrated to our new mail server on cPanel at some point. domain2.com contains mailboxes. domain1.com is setup within domain2.com on our old mail server as an alias/domain forward. From: @domain1.com To: @domain2.com. In cPanel I already have domain2.com configured with mailboxes etc..... It seems I can create the domain forward with domain1.com in two ways..... I could create domain1.com as a separate account in cPanel and then create the domain forward. Or, I could create domain1.com as a subdomain under domain2.com and setup the domain forward there. What would be the pro's and con's of either setup? I guess if customers have multiple domains you can organize them all under one account/domain but the subdomains aren't visible in the List Accounts so you need to know what domain they are associated with in order to find and configure them. If the domain is created as a separate account then it's easier to find. That's one downside to using subdomain it seems. If I created domain1.com as a separate account/domain rather than as a subdomain then I can easily locate it in the Account List. But in our example we don't have any email accounts to create under domain1.com as it's just a domain forward. So it would seem maybe best to create it as a subdomain under domain2.com. If I were to do that, is it best NOT to share the document root? Currently both domains point to the same web site, but if the customer wanted a different web site then sharing the document root would be bad, right? Anyway, just trying to figure out why you would want to create a domain as a subdomain rather than creating it as a separate domain/account in cPanel. What are the benefits or pros/cons of each method? Thank you.