What is “malefic”? In Sanskrit it is क्रुर (“krura”) - “rough, harsh, strong.” Malefic planets possess this nature, that is why they are called क्रुर or “malefic.” By contrast, “benefic” planets are सैम्य (“saumya”) or “gentle, soft, and generous.” What we really learn about life is that there is a right time and place for everything. There is a right time and place for energy that is strong and rough – and there is a wrong time for it. Similarly there is a right time and place for energy that is soft and gentle – and there is a wrong time for that as well.
What are the right circumstances for “krura” energy to use its brute strength? In astrology we express the answer to this question using the terminology of the houses. We say that krura strength is welcome and needed “in the third, sixth, tenth and eleventh houses.” What does this mean? It means that toughness and strength (which is what so-called “malefic” planets carry) is welcome regarding our own personal desires and ambitions (3rd house), how we deal with challenges and opposition (6th house), how we conduct ourselves in the unsafe public world (10th house) and how we go about earning profits for ourselves (11th house).
This is why classical astrology welcomes “malefic” planets into these four houses.