Usually, after Ubuntu is installed on a machine, the user adds various programs (via PPA, Ubuntu Software Center, etc), performs the regular updates (via the Update Manager), install/delete then reinstall a particulate application, ending with numerous unneeded packages that can make the system slower, or just waste useful disk space.
Days ago, Ubuntu Tweak 0.6 was released, introducing, among others, Janitor, an improved computer janitor, aimed at hassle-free "garbage" removal.
Janitor's main view is properly structured in:
- Personal, where all the thumbnail can be observed and deleted (not recommended because this process will start over when you open folders, recommended only if you have numerous broken thumbnails, meaning the thumbnails don't display the appropriate preview, usually due to a premature opening of folders with videos when you haven't installed the required codecs)
- System, here you will find the Apt cache (downloaded & installed packages), Old Kernel (previously used kernel versions) and other configuration and unneeded packages (recommended to remove all)