In which case they ALSO wouldn't have been able to figure out the markup which the template has replaced/simplified.
I don't think so.
A user sees an article that contains a nice little infobox, edits the article and sees {{Infobox Foobar|maintitle=Foo|subtitle=Bar}} The user wants to have a similar infobox in another article, only with an added subsubtitle.
Remark: If the user knows nothing about templates, he has a problem already. This was one of the reasons why the "templates used on this page" list was added.
So, the user goes to Template:Infobox Foobar.
Option A: The template is a plain-old simple template containing something like {| align=right ! {{maintitle}} |- | {{subtitle}} |} The user just copies the template into [[Template:Infobox Foobar extended]] and copy&pastes a single line in the table. Only the knowledge of table syntax is required.
Option B: The template is extremely powerful, general, using complex logic with many qifs, switches, etc. and comes with a two-page usage guide. In this case, the user is lost. He might once or twice try to copy a line containing subtitle, only to find out it does not work (maybe because it was in an if branch that is used only on even Tuesdays, or he forgot to wrap that line to another template so it ended in an invisible div, or whatever).
Note that I admit there are uses to complex templates, but they _do_ add complexity and raise the bar for (novice?) users.
-- [[cs:User:Mormegil | Petr Kadlec]]