Understand the person, frame the real problem, build something rough, and learn from their reaction.
Use when Use it on ill-defined problems where the need is genuinely unclear, where the people affected are not you, and where the cost of building the wrong thing is high. It is strongest early, when the framing is still open and cheap to change.
Avoid when Avoid it when the problem is well-specified and the answer is known — it is expensive ceremony for work that needs execution. It struggles with problems whose constraints are technical or regulatory rather than human. And it is the most ritualised framework in common use: workshops, sticky notes and a five-stage poster routinely produce the appearance of the method with none of the substance, because nobody left the building to observe anyone.
Not all features are equal: some delight, some merely satisfy, and some only hurt when missing.
Use when Use it when a roadmap needs to balance table-stakes against differentiation, when entering an established category where expectations are already set, or when heavy feature investment is somehow producing no measurable satisfaction gain.
Avoid when Avoid it in a genuinely new category, where customers have no expectations to classify against and the survey returns noise. It is survey-based, so it inherits every weakness of stated preference — people are poor predictors of their own delight. It is also expensive to run properly and stale quickly; a three-year-old Kano study is a historical document.