During development, one often saves considerable reload time by having local copies of QVDs instead of using files on network or server locations. (Stored locally in an encrypted volume, of course.)
Your first inclination might be to simply copy and paste the QVDs to your machine, but zipping the QVDs first yields significant compression, which will save you considerable time with larger files. (NB: Depending on the environment, you may want to copy the QVDs, then zip the copies, to prevent locking the originals from being used or reloaded during the zipping process.)
Recently, I wanted to grab three QVDs from a server, totaling 1.55GB. In addition to zipping the files, I was also curious what loading all of them into a single QVW and using QUALIFY * would yield in file size.
To my surprise, zipping was even smaller than the QVW with compression set to High by about 8MB…thus saving myself from the immediate need to write an “unloading” application, which would binary load that QVW, alias to remove field name qualification, store to QVD, then drop tables from memory.
So next time you are moving files, save some time and bandwidth and zip them first.