As a general rule of thumb: if the Available space on your Mac OS X startup disk is less than 5 GB, it is time to free some disk space. We suggest 5 GB as an absolute minimum as it generally requires that much free space to perform an Archive and Install of Mac OS X and still preserve some free space for VM swap files. However, more free space is better. For example, users of FileVault may want to retain more free space than that occupied by their encrypted Home folder as one requires free space larger than your encrypted Home folder in order to disable FileVault.