I like to know how much incremental disk space I'm using so I have a series of scripts that tell me the files which have been deleted/added and outputs to get the sum (yes, I know there are better ways). The impetus for checking disk usage is a tale in IT stupidity which I don't talk about! But now I use the script for other purposes as well such as verifying that my mirror has the same deltas without doing a full compare. I hope I haven't disappointed you with my usage :-)
I really should rewrite this but it was written many years ago and grew into something more than I originally intended. Plus, it works.