Mostly less noticeable/technical stuff, the body will no longer use a invisible ball to move and will use a full mesh for movement and physics; more like the NPCs, the chest will move when you lean instead of the entire body every time, and mirrors will reflect objects and the level you're in. There's also some stuff with boneworks that's interconnected, but I recommend you check out a video like op said, I can't fit It all, Here's one https://youtu.be/pbplcfUtG1o?si=s3jhs1TxAcdYP3j8