If your work involves regular contact with speakers of foreign languages, being able to talk to them in their own languages will help you to communicate with them. It may also help you to make sales and to negotiate and secure contracts. Knowledge of foreign languages may also increase your chances of finding a new job, getting a promotion or a transfer overseas, or of going on foreign business trips.
Many English-speaking business people don't bother to learn other languages because they believe that most of the people they do business with in foreign countries can speak English, and if they don't speak English, interpreters can be used. The lack of foreign language knowledge puts the English speakers at a disadvantage. In meetings, for example, the people on the other side can discuss things amongst themselves in their own language without the English speakers understanding, and using interpreters slows everything down. In any socialising after the meetings the locals will probably feel more comfortable using their own language rather than English.