Our spine consists of vertebrae and sponge-like discs. Gravity causes the discs to lose moisture throughout the day, resulting in a daily height loss of up to 1 to 2 cm (1/2” - 3/4”)! The moisture returns to the discs overnight, but not 100%. Over a lifetime, a person can permanently lose between 1 to 5 cm (1/2” - 2”) in height!
Many weight training moves (like squats & deadlifts for example) put a lot of additional pressure on the spine. Hanging from a pullup bar for at least 30 seconds is a fantastic stretch to help decompress your spine after an heavy weight-training session.