I use them more as a part of a larger research process than a specific method: it’s mostly (but not always) during very front-end research where the goal is to identify unmet, under-met, and/or unarticulated user needs in a focused domain. The cards are aids. Sometimes they’re helpful. They’re not always helpful. For someone you’re interviewing who needs encouragement or help in feedback or detail, they can jog thoughts. They’re are one tool in the quiver with lots of others.
There’s lots of cards, and there’s sets of cards, and of course, they’re not all applicable to every situation. For instance, I made the ones I show here for a design and research project in the CE domain, specifically around input. This particular project had both generative and evaluative components, and I used the cards for both parts.