In Joomla (CMS) the installation comes with a file called "robots.txt.dist". I know what robots.txt is used for, but don't know why a .dist version would exist. The install comes with a normal robots.txt which to me seems that makes the other file not needed.
Robots.txt.dist used for
joomlarobots.txt
Best Solution
.dist files are usually just an example file to get you going but aren't intended to be used as the real thing.