Mac OS X makes opening .zip files simple: you double-click them, and the OS quickly unzips them. But one thing has always bugged me: After I unzip it, the original .zip file—for which I no longer have any use—is still there. I'd rather my Mac clean up the zipped versions of files automatically after I expand them, instead of leaving me with one more thing to get rid of.
I'd known about the Archive Utility app—the Mac's default application for unzipping files, which only runs for the duration of the act of unarchiving and then quits automatically. And I know we've talked about tweaking its settings before. That's where I found the solution to my problem.
Archive Utility is really tucked away, in System/Library/CoreServices. Once I'd found it, I opened it and selected Archive Utility -> Preferences. There, I selected Move Archive to the Trash from the After Expanding drop-down. (I could have chosen Delete Archive, but that seemed too final. I could also have chosen to move unzipped archives to another folder—Old Zips, for example—if I wanted to maintain an archive.)
Once I changed the preference, I quit the app. Now, when I unzip files, the original zip archives vanish into the Trash, and I don't have to manage them manually.
There are plenty of other other options hidden in this Preferences window that you might want to fiddle with. For example, by default expanded files appear in the same directory as the archive itself. You can instead opt to put all expanded files in the same place—a folder on the Desktop, for example.