Parameter Templates serve only the following purposes at this time:
They can hold default information for the Site->Parameter configuration (EPA codes, reporting precision, graph min/max) to ease the configuration process.
They are utilized by certain reports to make the report configurations site-generic:
AirNow
Wind/Pollution Rose
Frequency / Concentration Distribution
Violation of Standards
E-mail Alarm Configurations (this would be the most likely reason you might wish to give an internal diagnostic parameters a parameter template!!)
They are used by the File Import Tool (optional) to make the import templates site-generic
They are used by the Automatic Data Validation Processor (optional) to make ADVP rules site-generic (same note applies regarding diagnostic parameters)