This extension allows the user to save selection on a text file.
Have you ever needed to save part of the text from a web page?
What you can do nowadays, is to save the entire page, with all the unneeded images and resources attached (a lot of things, for just some text) or to copy the text, open a text editor, paste it and search a path where to save it (a lot of steps!).
With Selection to file, today, you can simply select the text you want and click save: you will find all the text you saved in the download folder.