Climbers take their shoes off to reduce the pressure on their feet. This helps them reduce pain and prolong their session.

Climbing shoes are usually very tight, and, after wearing them for a while and climbing a few routes, they can get pretty painful. Taking them off in between routes allows the climber to reduce that pain and pressure from the feet.

This is more common in climbers who downsize their shoes, which means that they take a few sizes smaller than their actual street shoe size.