From the archive. We first published this in February 2013. The specific problem was in the Chrome of that era. The lesson still applies: when your disk fills up, check what is actually using the space before you start deleting.
I was cleaning up the drive on my MacBook Pro before an overseas consulting trip and noticed that Google Chrome was using a ridiculous amount of space. I use Safari almost exclusively, but I keep Chrome, Firefox, OmniWeb and a few other browsers around for compatibility testing.
Chrome was taking up 11.5 GB. A freshly downloaded copy was only 127 MB, so the copy on my disk was more than 90 times larger than it should have been.
What happened
It turned out that Chrome kept a copy of every old version of itself each time it updated, and never cleaned them up. My copy had collected 98 versions, going back to August 2011.
The fix
The easy fix was to delete Chrome and download a fresh copy from google.com/chrome. You could also open the app package and delete the old versions by hand, but that does not really save any time.
It is not a great idea for an app to grow like this without telling its users or giving them a way to control it. If an app on your Mac seems much larger than it should be, it is worth a closer look.