Not sure I buy that. Retracted scapula, engaged core, a few other things a PT could tell you makes the most efficient use of your posterior chain and thereby reduces fatigue and risk of injury
Can you get away with not doing it? Sure. Just like you can do deadlifts with a rounded back (to a point), or drive without using your turn signal, or swim using the doggy paddle. But is it good for you?
A good PT would also tell you exactly what GP is saying: You can’t just “fix your posture”— you have to change positions and move about every 30 minutes or more to avoid injuries.
Can you get away with not doing it? Sure. Just like you can do deadlifts with a rounded back (to a point), or drive without using your turn signal, or swim using the doggy paddle. But is it good for you?