text: Synarthrosis are non-movable boine joinings-like the skull, ribs, and sternum- These are places where there are no mobile joints, where you don't require movement.  However, they do lend some flexibility to the bones, so your skull isnt like an eggshell that shatters, but has some freedom of motion.  Obviously, for your limbs, fingers, etc, you want freedom of motion-these types of bone-to-bone connections are called diarthroses, like the ball and socket joint of the shoulder, or knee joints- You need large range of motion here.