We used the passive
- when the person or people who do the action are unknown, unimportant or obvious from the context. Linda's purse was stolen. ( We don't know who stole it.) The car is being repaired. ( i's unimportant who is doing it.) The robber has been arrested. (It's obvious that the police arrested him)
- when the action itself is more important than the person/ people who do it, as in news headlines, newspaper articles, formal notices, advertisements, instructions, processes, etc. - The annual meeting was held on March 20th
- when we want to avoid taking responsibility for an action or when we refer to an unpleasant event and we do not want to say who or what is to blame. - four people were injured in the bank robbery.