If you are using the Servername and database name in the connection strings in all the applications connecting to your database being migrated, this process gets tough and tedious to update once the database is migrated to a different server. It is always advised to use database DNS in the connection strings instead of the IP address or the Servername.
This also applies to the report server datasources as well.
I know it is hard to make the change but if the change is good, it is worth the effort.
I think this starts to get tricky as the number of servers and instances increases, especially if your DNS records differ considerably from your server names. Still, I completely agree: using CNAMES makes life a lot easier.