In the databooks or by Kishi?
She seems to give Sakura a secondary source of chakra, makes her immune to genjutsu (she was just exhausted when sasuke used that move on her, she fell asleep before he even did it) and seems to contribute to why Sakura is so intelligent, to quote Ino "She has two minds". Inner Sakura is basically a bujii without the downsides and her disappearance in part 2 just means Sakura conquered her.
She seems to give Sakura a secondary source of chakra, makes her immune to genjutsu (she was just exhausted when sasuke used that move on her, she fell asleep before he even did it) and seems to contribute to why Sakura is so intelligent, to quote Ino "She has two minds". Inner Sakura is basically a bujii without the downsides and her disappearance in part 2 just means Sakura conquered her.