How does the Loop of Henle help an animal living on land?
An animal living on land is always losing water by evaporation. It doesn't lose solutes that way, though - so its blood is always getting more and more hyperosmotic.
This animal needs a way to save water from its urine, but let the solutes go out! That's hard to do, when the only way it can move water is by making the water follow solutes.
The Loop of Henle allows an animal to retain water alone. It does this by pumping salts into the part of the kidney surrounding it. This creates an area in the kidney which is always salty - the renal medulla.
Now when urine is passing down the collecting duct, on its way out of the kidney, water can be pulled out of the urine to the salty, hypertonic renal medulla. In this way water alone is reabsorbed from the urine in the collecting duct, and the solutes go on out in the urine!