When you want to start measuring or analyzing something, quite often you have no idea what kinds of results to expect. Often, you take whatever comes out of your SQL (or BI report) as truth. "OK, so our performance did grow 20000% last month..." (OK, maybe not that extreme). But how can you be sure? There are so many things that could've gone wrong - the quality of data, incorrect assumptions, error in a query... Even such trivial as missing up asc and desc. Be cautious!