Rope Craft

Finishing up Rope Craft and I'm trying to reinforce the importance and uses of the various knots, but I'm having trouble doing that with two of them. The Two Half Hitch and the Tautline Hitch. They seem very similar in both use and tying, so what really differentiates them from one another? Obviously the Tautline Hitch seems a little more hardy simply because it has an additional step. What am I missing?

As a side note, the knot that seemed to the boys at first to be useless, the Sheepshank, I was able to explain ways that it was extremely useful. It was fun to see their expressions change as I explained the uses.  

Sheepshank is the hardest one to teach the boys.

Any insight into the differences between the Two Half Hitch and the Taut line Hitch?

Taut line is a prusick type knot we use on adjustable tent guy wires.

two half hitches are just a quick knot to tie something off. It's not adjustable. A half hitch is more a rope dressing for the end of a rope to add a little safety after the knot to secure the loose end of the rope so the knot won't come untied.

Mark Jones

They both are able to slide down the rope when I tie them (tightening the loop). How is the tautline more adjustable than the two half hitch? Is the taut line supposed to stay where you place it, even under tension, whereas the two half hitch will continue to tighten the loop?