The decoration blocks exist purely for vanity. They may only survive on a dirt block and, much like grass, will disappear without a source of light. You are unable to stand on a decoration block, but you may walk through it freely with no hindrance to movement. Their only purpose currently is decoration.

They can also be used to block water. Water will not pass through them while the player still can.

Without sponge blocks, the decoration blocks can be used to fill the space the player is standing in when filling a flooded area in a confined space, after the rest of the water blocks have been filled in.