A free end shaft has 2 degrees of freedom plus rotation. For instance, if you insert one end of an Acme screw in a flanged end bearing and hold the other end of the shaft you will be able to freely move it in 2 directions.
A fixed end shaft only allows rotation. If you add a second flange bearing as shown in the photo above, you will no longer be able to move the free end of the screw without bending the shaft.
