This depends very much on your environment.
If you plan to run SSL you should have a separate FQDN for each tenant hosted by that machine / cluster. ConfigDB is also a tenant and therefore would need it's own FQDN. If you plan to run without SSL this is a bit more relaxed and can really be any value, but it's best to have it be a machine name or alias that points back to this server.
That said, this application is built for the cloud and you can actually scale out the load for each module to it's own server / cluster. This includes the Central config, so if you choose to host it elsewhere, set the appropriate hostname / FQDN.
The install guide does cover this in much deeper detail.