Wikipedia:Substitution trick

Some templates return a cleaned-up copy of themselves upon substitution. This is known as the substitution trick or subst trick and is especially useful for removing unsupported parameters (which may cause a page to land in a maintenance category) or updating a template to use the current names for parameters instead of their aliases.

Module:Unsubst offers a straightforward tool to carry out the subst trick.

A prominent example of a template that can perform the substitution trick is Infobox album and some of its associated templates like Singles and Extra album cover. Other examples include most maintenance templates like Citation needed and Unreferenced, which when substituted will generally add the date parameter with the month and the year.