The Galaxy S23 Ultra also lets you take 50MP images, which take up less space than 200MP pictures but contain more details than a 12MP file. While a 24MP image will probably take up more space than 12MP, the increase in quality will likely be worth the increase in storage requirement, which we assume will be more practical when compared to 50MP and 200MP shots.
The main camera may also have a neutral density filter for 24MP RAW pictures. It will be like the Expert RAW camera app’s neutral density filter which helps reduce the light entering the lens and prevents overexposure. This will allow for better photos in bright environments.