1. The passive voice is often used to change the focus of attention from the acting subject to the object of a current action.

2. Sometimes we are not interested in who perform an action  (or it is not necessary to know).

3. The passive voice is very often used when we describe a process or procedure because we are less concerned with who has done something that with what is done.

4. Changes of state and completed actions are described using the present perfect passive.

5. When writing in a formal business style, more emphasis is placed on the message itself rather than the writer, in other words the style should be impersonal.
An impersonal style is achieved by using the passive and, in particular, by beginning sentences with It ...