Why does Harry use the Patronus Charm in "Harry Potter and the Prisoner of Azkaban"?
To repel Dementors and save Sirius Black.
<s>[INST] <<SYS>> Answer as briefly as you can to the following question. You are required to give a one-shot answer: <</SYS>> Why does Harry use the Patronus Charm in "Harry Potter and the Prisoner of Azkaban"? [/INST] To repel Dementors and save Sirius Black. </s>