de similar boards to these in the first building game I played, they are useful in building layout.
The purpose of the boards is to allow you to set all of your building materials out in work area, where you can view them side by side.
Seeing all mat's at one time allows you to compare colors and textures and decide i.e.: what wood grain blends well with what stone, tile, plaster, metal and the rest.
If you are on a Survival server, the boards will allow you to work with the boards by the comparison method only.
If on a Creative server: you can interact with a Builder Board, by picking a block of material and using your sledgehammer to minimize that block. Pick up the block and place in your inventory hot slots #1-5. That one block will now continuously supply you with as many blocks as you need to construct with. Don't forget to replace that block that you picked, back into the builders board for future use.
Note that the wood material, at this time, can not be hammered and recovered as the stone can. But, I think Red said that we will be able to do that after updates.