Est run time: 10-15s.

Usefulness: We've all had that experience where we needed to send a PDF last minute only to get a warning from Google that the file is too big, and by the time we finish reading the error message, the deadline has passed, and now it's yet another season I won't be on American Idol.

Caveats: If your file is already compressed, the tool will not make a difference - and may even increase it by a few KB.