This is an auxiliary template allowing to encode "
|" within template parameters. It is unnecessary to get a "
|" is a better choice for this purpose. However, the "
|" delimiter for a Wiki table must be escaped by a template for use within a template; see also 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.
For obvious reasons this is a high risk template, and it cannot be substituted.