I use spacesniffer to find any lost space our machines, typically when I get a report of machines sub 5GB. I've found it extremely useful to incorporate into lansweeper. Go to the below site and download the .exe once downloaded stick it into your Lansweeper\Actions folder and use the following
I don't believe there is a way to do a "quick" scan, but if you know you have particular trouble areas like roaming profiles, you could change the following to point directly at the users folder or w/e folders you tend to have the most trouble with.