Marcel Halstenberg is a left-back and he doesn't seem to have played much at Leipzig either. I think it's quite natural that he wants to leave Leipzig, moreover he has other reasons such as wanting to live closer to his family if he joins Hannover. Statistically last season, Marcel Halstenberg didn't shine so brightly because he only managed to score 2 goals and 4 assists, but indeed the left back position also doesn't need to do anything excessive, the important thing is to be able to focus on maintaining defense is the main key.
The transfer fee is also very cheap € 500k, even though the market value is around € 3.5 million. I don't think Leipzig can make anything out of this transfer and at least they will try to bring in another left-back to cover for David Raum.