There is a feature in Bridge that allows you to batch rename files while preserving the original filename as a new field in the metadata. This feature would be great to have in Lightroom as well, most likely as a checkbox option under "file renaming" of Export. When dealing with loads of files, it ensures that no matter what the file is renamed we will always be able to track back to the raw file. I saw someone posted about this 10 years ago in the adobe forum so I am guessing that it isn't super important...