The ahh slide is an extremely helpful exercise to help release tension on the back of the tongue. Tension on the back of the tongue causes limitations on your range, both high and low notes, creates a swallowed tight vocal sound, and inhibits your best singing sounds. This exercise should be practiced for short amounts of time, several times each day. We are trying to let go of old muscle memory and create new, so repeating the exercise often will help you achieve the new muscle memory more quickly.
When possible, do this exercise in front of a mirror to make sure your tongue is not engaging as you make the sound. Have fun!