Ever needed to share VirtualBox machines, transfer them over the internet or back them up?
This article describes how to reduce the size of your virtual machine hard disk. Space savings are incredible, especially if you've been adding/deleting files to the VM hard drive a lot.
What the article does not say (because it is obvious): zip your virtual machine after performing the described steps and before transferring/backing it up.
Link: How To Shrink Your Virtualbox VM And Free Up Space For Your Hard Disk - Make Tech Easier