What is the difference between both communities? Even my reputation and number of badges are different in both communities. Do I want to follow both? What is the major advantage(s) if I follow both communities?
Database Administrators is the main Q & A site.
Database Administrators meta is "the part of the site where users discuss the workings and policies of DBA Stack Exchange rather than discussing database administration itself".
See What is "meta"? How does it work? in the Help Centre.
Just to address a couple of other points:
Your reputation should be the same on both sites, but can sometimes appear to be slightly off due to synchronization and/or caching, because in some areas on the sites the number can come from different places (in the past there have been ways to see this even within a single site, but those do generally get addressed over time).
On the main Stack Overflow site, its meta site was originally completely separate, including reputation, but they fixed that by making it follow the behavior of other sites with a meta site for discussing policies etc. for Stack Overflow on its own (meta.stackoverflow.com) and splitting off the original meta site into a "meta meta" site for discussing policies etc. for the entire network (meta.stackexchange.com).
The badges are tracked separately. This is likely to encourage similar activity and patterns on the meta site as well, rather than dismissing things like editing or flagging because you already have those badges.