HTML 5 - Why enctype text/plain value is not recommended?

This video explains why is not a good option to use the value text/plain as enctype value. Using this encoding type and PHP, data is sent as a string and it may be difficult to process in certain circumstances.
In the video, we're editing the document from the server. The normal procedure is to use a client and load the file to the server using an FTP client application.
Server script language: PHP version 7.0
Editor: Brackets
O.S.: Linux Debian Version 9 (Stretch)
Web server: Apache Version 2.4.25