I've been using it for the opposite reason: I'll see something in a news story and want to search on it for some background, and all I get are 500 copies of the same news story or commentary on it. Being able to exclude anything from the past week or so makes it easier to filter all those out. It is slightly more awkward to use it that way UI-wise, though: there are quick links to press for "last X hours/days/etc.", but no quick way to get "older than X" without typing stuff into the "custom range" thing.