Logic is a much less cut-and-dried affair than many text-books suggest.
Formal logic constitutes a "body of knowledge", not in the sense that all its findings are incontrovertible facts but somewhat in the same way as moral philosophy.
wo further considerations are often given as reasons for studying logic:
Logic is "therapeutic": one learns logic in order to become better able to recognize and to construct good arguments (in philosophy or any other discipline).
Formal logic is an indispensable item in the contemporary philosopher's toolkit.