Many times on a Windows Server or PC you will have had multiple users log in at some point in time, and each user account has it’s own Recycling Bin. When getting cramped for free space, it can be handy to empty all Recycling Bin’s at one time, so you do have to, or can’t log into the other accounts:

Windows7, Server2008/R2, Server2012/R2

rd /s c:\$Recycle.Bin

WindowsXP, Vista, Server2003/R2

rd /s c:\recycler