Having restricted joint mechanics through length tension imbalances of your muscles is a great way to force the body to create compensatory movement patterns that will affect your timing and performance.
If you are stuck in thoracic flexion (like my guy below with forward head posture, rounded shoulders, and an upper thoracic spine that just doesn’t want to extend), your ability to extend into your pop up and land both feet on your board at the same time is going to be tough. It also means that you will have altered spinal mechanics limiting spinal facet joint rotation. In real world terms, this means you will not be able to counter-rotate your trunk and hips into a bottom turn without compensating with your hips and knees causing muscle strains and connective tissue sprains. All of the above will lead to overuse injuries.