After the fluid, carbs, and sodium have been absorbed, the sodium helps keep the fluid in the bloodstream instead of getting filtered out by the kidneys to become urine.

For example, Maughan and Leiper (1995) found that the percentage of fluid retained increased progressively as beverage sodium
concentration increased from 2 mmol/L to 26 mmol/L to 52 mmol/L to 100 mmol/L, urine output decreased. Urine output was inversely correlated to sodium content.

Studies show that having carbohydrates and sodium in a beverage helps the water transfer from the intestine into the bloodstream faster (Murray & Shi, 2006).
Faster absorption feels better in your gut and gets the fluid out into the body where it is needed most.

HY.Q tastes so good, you’ll drink more. Studies show that when athletes are given hydration drinks similar to ours or water during exercise, they drink more of the hydration drink (Minehan et al., 2002).

This is the most important aspect of minimizing dehydration. Because these athletes drank more, they were less dehydrated.