Not just for formal testing
Mark Hurst has a great column about Four Words to Improve User Research. He's writing from the point of view of a rigorous UI/design tester. I think the mantra needs to go much further though--looking at the world through a different lens.
I got a call from a hospital, pestering me about a bill I'd gotten a week earlier. The caller then said, "I need to know your birthdate." Why, I asked. "So I can prove I spoke to you."
Of course, I don't care at all about their systems or their management tools or their productivity. I don't care that someone thought this was a clever way to manage their many callers. I just know that telling this guy my birthdate wasn't going to help me at all, so I said no.
When people interact with your site, your product, or your company, you don't have the luxury of telling them a story first. You don't get to give a speech about WHY it is the way it is. It just is. So the experience must stand on its own.