Mud, dirt and water flicked up from the rear wheel - eventually ends up in your frame. That scratchy sound when you have to adjust your post - not nice. The Bikeyoke Willy, creates a water tight seal around the clamp and frame - everything stays clean less and less faff when you need to adjust things - picking out the grit in the clamp threads.
Does not just work with Bikeyoke seatclamp - any bolt on clamp with a diameter 30.9-31.6
Note: Works best with clamps that have low profile bolts and smooth edges and it can tear the cover.