The best thing about plain text is its longevity and portability. You can be sure that a plain text file you make today will still be easily readable and compatible with all devices even after 40 or 80 years of computer and software evolution. You won’t have to dig up some long-forgotten app or look for some obscure conversion script in order to read it. No matter how much software has changed, you’ll still easily be able to open and read your plain text files, same as you ever were.