This would be huge for DB monitoring.
It is possible to have multiple instances of just about any RDBMS (DB2, MySQL, MS SQL, Oracle, and PostgreSQL) running on the same server but on different ports (and we frequently do here).
To make things even more complicated all of them (except Oracle) allow you to have multiple DBs in a single instance, which makes trying to set up monitoring a difficult task since there is no one-to-many relationships for templates.
If there was a way to be able to have some type of hierarchy of templates for a single host with parameterized templates this would make it far easier to set up monitoring.
I bet there are other applications that could also benefit, such as Java.