Template talk:Error:must be substituted

According to Special:WhatLinksHere/Template:Error:not substituted the template is unused. Does this mean the template works well and all inclusions are always substed or does this mean the template is not used at all? If there are templates which use this template in a <includeonly> area (so it won't appear on WhatLinksHere), then please link "Template:Error:not substituted" in the documentation page for that template so that the use of the template is traceable through WhatLinksHere. --Slomox (talk) 14:57, 16 January 2009 (UTC)