The fundamental idea of a walkthrough is to think as the user would, evaluating every step of a task in an interface for usability problems.
I think this is a smart way to find problems in a design. Walking through a task as if you were the user helps spot confusing steps or areas that need improvement. I agree that this method is useful because it focuses on the actual experience of using the interface. However, it might not always catch every issue since real users may think differently than the person doing the walkthrough. That’s why combining this with real user testing could give a more complete picture of usability.