I wanted to move a large number of files from one directory to another, but the target directory already had many of the filenames already used. This is a common enough problem -- digital cameras use
DSC#, video downloaders often append numbers to get a unique filename, and so on. In both those examples, the sequence restarts if you empty the program's work directory. So, you'll end up with
DSC0001.jpg every time you empty your camera's memory card. If you're trying to move such files into a single directory, you'll get conflicts every time.
Instead of manually renaming the files before transferring them, I wrote a simple script to give each file a unique name in the destination directory.