Sasuke is missing his left hand in Boruto: Naruto the Movie. In the manga, Tsunade gives him a new hand but he gets it removed. Why?
Sasuke refused tsunades offer for the arm to remind himself of his sins. This is quoted straight from the manga.
Taken from the Naruto Wikia :
Sasuke loses his left arm at the end of the Fourth Shinobi World War, though unlike Naruto, he opts not to have it replaced with a prosthetic that was being prepared for him.
According to my opinion, he just wanted to keep that lose to remind him of someone who is always willing to go to great lengths too save him (naruto). Also he shouldn't see the world in darkness as he used to in shippuden. While naruto accepted Tsunade-hime's help to have an arm, he was being a little emo here. After all it was the biggest event in his life.