This is an auxiliary template allowing to encode "
|" within template parameters. It is unnecessary to get a "
|" in these cases, better use "
|" for this purpose. However the "
|" delimiter for a Wiki table has to be escaped by a template if it's used within a template, see also w:WP:QIF.
Note that there's no such problem with "
!" (exclamation mark), it only affects "
|" (vertical bar) in conjunction with the m:Help:Parameter default mechanism within tables.