Main templates have code that detects when a record is imported to the database and disables the output to avoid redundant display of information. These templates remain useful for content that has not yet made it into the data dump. Some are used for content that is not and never will be in the database.
Linkers are used for item links to provide colorized links, and for any group of pages that WILL or MAY get a database someday but don't have one yet. Once a database and/or a namespace has been established for a group the linker should be deprecated but maintained so that older pages will still work.