If you happened to link a file simply to an Asset (like suggested on this link), and then would like to make a version of the same Asset, say linked to a task so the file is then taken into the version's pipeline ect, you will find your self forced to reload the file for the version. This doubles space in your servers with identical data but mostly, it doubles upload and user time without really seing a solid reason for not being able to share the already uploaded file.