Some templates are only used to save keystrokes
(http://en.wikipedia.org/wiki/Template:User is a good example) or are otherwise
. Rather than force the servers to go through all the hoopla in keeping cached
copies up to date, etc., or trying to discourage users from making such
templates (pointless) allow templates to be marked as substitute-only, the way
signatures are handled now.
Doing this through an edit would be best, so some sort of marker (<!--subst-->,
for example) that tells the server to just subst: the included template even if
subst: is not explicitly used.