Page "XML Signature" Paragraph 32

Moreover, if an XML document is transferred from computer to computer, the line terminator may be changed from CR to LF to CR LF, etc.

A program that digests and validates an XML document may later render the XML document in a different way, e. g. adding excess space between attribute definitions with an element definition, or using relative ( vs. absolute ) URLs, or by reordering namespace definitions.

Canonical XML is especially important when an XML Signature refers to a remote document, which may be rendered in time-varying ways by an errant remote server.