There seems to be this idea going around that usability testing is bad, or that the cool kids don’t do it. That it’s old skool. That designers don’t need to do it. What if I told you that usability testing is the hottest thing in experience design research? Every time a person has a great experience with a website, a web app, a gadget, or a service, it’s because a design team made excellent decisions about both design and implementation—decisions based on data about how people use designs. And how can you get that data? Usability testing.

Jared Spool will tell you for free that when his company researched the causes of failed designs, they found that lack of information was the root of all bad design decisions. The point of user research is to make good, solid, confident decisions about design. Why usability testing as opposed to using other methods? I contend that 80% of the value of testing comes from the magic of observing and listening as people use a design. The things you see and the things you hear are often surprising, illuminating, and unpredictable. This unpredictability is tough to capture in any other way.

The other 20% of the value comes from the pre-testing discussions team members have as they decide what their Big Questions are and the post-testing discussions about what to do with what they’ve learned.

via A List Apart: Articles: Usability Testing Demystified.