Running apt-get commands on a Debian-based system is routine. Packages are updated fairly frequently and commands like apt-get update and apt-get upgrade make the process quite easy. On the other hand, how often do you use apt-get clean, apt-get autoclean or apt-get autoremove?
These commands clean up after apt-get's installation operations and remove files that are still on your system but are no longer needed – often because the application that required them is no longer installed.
The apt-get clean command clears the local repository of retrieved package files that are left in /var/cache. The directories it cleans out are /var/cache/apt/archives/ and /var/cache/apt/archives/partial/. The only files it leaves in /var/cache/apt/archives are the lock file and the partial subdirectory.
Thanks to Sandra Henry-Stocker (see source)