Adding and removing files in VirtualBSD causes its disk usage to increase/decrease accordingly but, due to the nature of the expanding virtual disk, the virtual machine itself will keep using more and more of your computer's disk space.
In other words, no matter how many files and folders you delete in VirtualBSD: once you've added them, the virtual disk won't shrink back automatically. Still, you can recover the unused disk space by following these steps:
1) Open a terminal (right click anywhere on the desktop and select Terminal from the menu).
2) Type the following command (remember, cut & paste is your friend):
su -m root -c 'vmware-toolbox > /dev/null 2>&1'
3) Click on the Shrink tab, then click on /, press either Shift key and click on /var to select all the four lines. Finally, click on the Shrink button in the bottom left corner:
4) Confirm the operation by clicking on Yes:
5) A somewhat lengthy process will start and this bar will be (slowly) filling up -- four times:
6) Now that the preliminary work is done you can start the shrinking proper by clicking on Yes:
Note 1: Ignore messages like /usr: write failed, filesystem is full -- they're not nearly as bad as they seem.
Note 2: The operation will take a few minutes and the Virtual Machine will be frozen for the whole duration.
7) Once you are back in control, dismiss the last dialog and close the application by clicking on the close Close button in the lower right corner of the main window (see top of the page).