With CS qualification you may join CA to convert yourself into a complete package of lagal and finance person. With CS+CA combo you can also get the chance to work with top management level. CA is a very good combination with CS because overall approach required for both the courses is same. With CA you can handle all the finance functions of a company.
With additional CA qualification you can easily and confidently handle Finance work/department along with the secretarial work/department. Later on you may be get promoted to legal and secretarial and finance head.