From http://www.forum64.de/index.php?thread/65795-an-alle-die-mit-vice-arbeiten-oder-sonst-einem-emulator/&postID=1031196#post1031196:
Be able to read a specific block only, instead of reading complete tracks. This is interesting especially in case of damager disks, where one wants to retry specific blocks until they can be read.
Moved to https://github.com/OpenCBM/OpenCBM/issues/56, closing.