Along those lines... I was once asked to essentially "speed up a report" but after asking a few questions discovered that the user of the report actually needed only about two values out of dozens of pages of detail and summarized totals on the report. Everything else on the report had been thrown on in the initial design as "someone might need that" requirements.

We created a new report that delivered what the user actually needed, and it ran in a fraction of the time. The speed difference was so great the users in fact doubted that the report could be correct, until they verified it against the old one.