Mechanism of Concentration of Filtrate

The loop of Henle, together with the vasa recta, sets up the counter-current mechanism that builds an increasing osmotic gradient in the medullary interstitium (from about 300 mOsm/L in the cortex to about 1200 mOsm/L in the inner medulla).
This gradient allows water to be reabsorbed from the collecting duct, which produces a concentrated (hypertonic) urine. Mammals can thus conserve water.
Without the loop of Henle, no medullary gradient would form. Water could not be withdrawn from the collecting duct, so a large volume of dilute urine would be formed. Filtration would still occur, so urine would still be produced.
So if Henle's loop were absent, the urine would be more dilute.

The loop of Henle, with the vasa recta, creates an increasing osmotic gradient in the medulla by the counter-current mechanism.
The longer the loop of Henle, the steeper the medullary gradient and the more concentrated the urine that can be produced (e.g. desert rodents have very long loops).
So the concentration of urine depends on the length of Henle's loop.