Some do standalone display. Some build the keyboard around the cap as a concept. Some just mish mosh it up. Some try to get a bunch of them from the same series for a more uniform keyboard layout.
Basically all kinds of things. I've got a couple, mostly they sit in a case and cover, when I feel like one I may switch out my keycaps. I won't buy something without a specific layout in mind, personally, but different strokes for different folks.