If you have multiple BFS volumes on your system, and if you’ve changed your primary boot volume at some point, you probably have a giant swap file hanging out on the old boot volume(s) that’s no longer being used. Open a Terminal and type:

cd /old_boot_volume/var
ls -l

You should see a file called swap. If you’re sure this is not your current boot volume (and you don’t intend to use it as a boot volume again in the near future), type:

rm swap

If you use a disk space utility like FreeSpace, you’ll immediately see a massive gain in reclaimed disk space. Because swap space is created automatically at boot time, this is not a dangerous procedure.
This tip is classified as a Warning because BeOS does nothing to guard against the storage of huge, unnecessary swap files, nor does it warn you about their presence.