Currently, players can make one via a glitch at the world border by using a piston to push one slab into another, but as a full feature it could expand builds in a unique way!

Perhaps this could also open up the possibility of combining different slabs making full blocks? For example, having the bottom half as an oak slab and the top half a stone slab! This would allow for lots of creativity in builds and possibly open doors to very unique structures in the future!