RFC 2822 defines the Date: header. It declares the header a required part of an email message. The syntax for date headers is clearly laid out. Stil, even a perfectly planned world has storms. The truth is, many programs get it wrong. Very wrong. Or, they don't include a Date: header at all. This often forces you to look elsewhere for the date, and hoping to find something.
For this reason, the tedious process of looking for a valid date has been encapsulated in this software. Further, the process of creating RFC compliant date strings is also found in this software.