if you got a large collection of .adf, .dms, .dsq, .lha.. of same stuff, a lot of disk space can be freed by unpacking it (as much as possible), then repacking all in giant solid .7z (for eg.) using large dictionary.
its somewhat harder, if you want to be able to reverse the process later. (metadata like timestamps, comments, etc. must be saved then).
hdds are cheap, but it should be easier to backup, search, check data if its smaller.
