When done poorly, it means you get trapped in a room with some folks with religious zeal and a set of post-it notes in various colors, sharpies, and colored paper sticky dots for a few days. Afterward, you get... not much. It's just like agile.... if the "practitioner" is hyper-focused on the rituals and ceremony, it's easy to miss doing actual work.
My personal beef with the concept is that the ceremonial aspects mean you need a special UX/design/etc specialist, who comes in and leaves. Usually the "design" processes focus on 80% solutions, and nobody comes back to finish the other 20%. You used to notice this when people built out responsive websites -- key functions that weren't in the "Top X", would just disappear on mobile.