Full user review
"The program you never knew you needed until you had it"
Allows you to see which folders or file types are taking up the most space, making it easier to grok the true makeup of your computer's storage. Not something you need to run on a regular basis, but once you are used to having it around, doing disk cleanup will always feel like it's missing something without WinDirStat.
Yes, it does take a while to scan the drive or folder you ask it to inspect. But personally, I prefer this to something that runs all the time in the background, especially since you only need to use it every once in a while.
The user that claimed this isn't free must be on the wrong page or something, because you can even download the source code from *multiple* repositories (SourceForge, Bitbucket, GitHub). See http://windirstat.info/download.html for details.