in my experience
One example of that is people looking for "qttask" in Google, who find this page which doesn't mention that term. but when Google indexed that page last, the was a Communiblog entry with that term in it, so people land here. That's not a great user experience, so I'm going to mention qttask here, so it gets indexed in this page (and for the record, the home page here has a "no index" rule, and tells robots to follow links to individual archives and index them) and people can follow this link to directions on how to remove/disable qttask.