Unlike wireframing, start without graphic design concerns. No layout. No screen sizes.
In effect, stay focused. Devise the elements and their progression with all of your mental room.
In contrast to mockups, explore and iterate ideas with more accurate usability feedback.
Likewise, communicate. Explain what you're trying to achieve in a clear and functional prototype.
Try out page flows, groupings, and progression alternatives on the fly.
Experiment with different labels and UX writing practices.
Discover edge cases early on.
Convey complex requirements in a tangible live spec prototype.
Make the graphic design phase feel more familiar and direct.
Plan a little bit,
save a lot of rework.