You would want to configure to show file extensions for a couple different reasons. First if you have a couple files and they are have the same name but one is say a PDF while the other is a DOCX file. Another reason, mainly for development, programming, graphic design, ect. you may need to know different extensions to determine the language a file is written in such as PHP, HTML, ect. or to know an image type such as jpg, png, gif, ect.
