The real benefit of the sheepshank for shortening is that you can put one in the middle of a line when both ends are already attached to something, then slide it to adjust the length as needed.
As for the clove hitch, again the real benefit is that you don't need access to the end of the rope. Particularly useful when stringing out a rope fence, for example. It's also strongest when there's roughly equal loading on both sides, which fits nicely with being able to tie it in the middle of a line that's anchored at both ends already.