One of the reasons (there are many reason but this is just one) why we would like to change an active sentence into a passive one is because we would like to bring the object of the sentence into focus. Consider these sentences:
- My brother was hit by a car.
- A car hit my brother.
The focus on my brother is far more important than that of the car. So it would seem logical to put my brother in the subject position of the sentence, as in 1. The subject position should be seen as being reserved for more important information, or be the focus of the sentence. So if the sentence becomes a passive structure let it be so if it is appropriate. But when the choice of active or passive is an equally valid one, choose the active. The active is usually clearer and more efficient.