Since there is no easy way to determine which repository files are not needed so you can do some sort of ''cleanup'', it is not recommended. Also, in ALL current versions of QC (11 and later) the repository is compressed and encrypted (optimized), so you can't even make any sense of the file names anyway.
Generally, people just add disk space or a new drive. QC does NOT like ''mapped'' drives, by the way, but you *could* use a network location.
You can change your BASE REPOSITORY PATH in Site Admin parameters so that NEW projects will have repositories there, but be careful in QC11.52 and later- see this post:
If you have one or two projects with large repositories, it is possible to MOVE the repository for a project without changing the BASE REPOSITORY PATH. This will effectively ''split'' your repository location out to an additional location for a few projects, AND you need good notes about having done this when it comes to re-combining all repositories (best practice) when you upgrade in the future to a NEW server with sufficient disk space for the ever-GROWING repository.
To accomplish the split;
Do a REMOVE for a project (temporarily taking it out of your project list), then you can MOVE the entire project repository (Use a tool that can do a verify of the copy to make sure you copied ALL files and that they are IDENTICAL) to a different drive (C, E, or ''\ (computer) (shared-path)'' for instance - usually keeping the same path except for drive letter), then EDIT the project's DBID.XML file in that resulting repository folder so that it's ''PROJECT_DIRECTORY'' tag has the NEW path, then RESTORE the project.
This will result in freeing up disk space used by your project on drive D and now using space on the other drive.
BE CAREFUL later when you upgrade as all of your projects will not be using the SAME relative repository path -- just make sure to copy them all into the NEW server's repository path and you can change the ''Project_directory'' path again at upgrade time.