Reader T.E. Watson (who also happens to be writer-of-lovely-children’s-books T.E. Watson ) has a childlike wonder about OS X’s receipts. He writes:
I was going through my system and came upon a folder called Receipts. It has a million different packages in it and it appears to be a lot of what I have installed at one time or another. Is it safe to dump the folder and not have any adverse effects on my applications or system operations?
It depends on how finely you care to parse “adverse effects on my applications or system operations.” If you dump the contents of this folder your applications will continue to march along as they always have and you won’t notice a difference in system performance. Until…
…you run Software Update or one of your applications checks for an update. The items in the Receipts folder are exactly that, receipts for updates you’ve installed. OS X’s Software Update, as well as other application’s updaters, drop these smallish files into the Receipts folder so that when they next look for an update, they know what’s already installed. Should you toss out these receipts, Software Update and other applications may attempt to download and install software you already have—even versions of that software earlier than what you have.
In most cases it’s best to just leave these files alone. They don’t take up a lot of space—I’ve got 191 of the little suckers and they eat up 258MB—and the confusion caused by trashing them isn’t worth it.
However, if you feel like an update didn’t “take” you can trick Software Update into giving it to you again by tossing that particular update’s receipt. Or, if you’d like to have a copy of the updater file, you can move its receipt, open Software Update, enable it for download, and then choose Update -> Download Only. Do this and the updater downloads to your Mac without installing.