Rotatable half block
One whole block is for some purposes too thick to use as a wall part. Structure frameworks consisting of beams and logs which are thinner than a whole block get hidden in the one block thick wall or only visible in either side. Many users resize the beams into a half block shape and size and use them as wall parts to tackle this problem. It could be more convenient if half blocks themselves could be rotated and used as wall parts.
Half slanted/half normal block stacking
You know this problem when you build a roof you can't stack a half slanted block onto another of different material into one full cube space so the side of the roof slant has stair case look, not a straight line.