This is a simple search, and a simple fix, but I just had to re-learn it so I'll post it here.
When performing a disk cleanup on any machine older than two days, you'll probably be forced to wait for several minutes for the process to compress old files. If this is important to you, enjoy a free coffee break. If, however, the gain is not worth the wait, you can eliminate this step from the process.
Go into the Registry and navigate to this key:
And then delete the subkey "Compress old files". The Google search for "compress old files" registry contains more detailed articles on this.