Hi
That's an interesting question.
It is true that the active voice is clearer because it focuses the reader's attention on the "doer of the action"; it is also more concise simply because it usually involves fewer words. But there are a few instances when it is preferable to use the passive voice.
One use of the passive voice is to make a negative statement sound more polite. A mistake was made sounds better than You made a mistake. Using the passive voice here helps avoid pointing the finger of blame at someone.
The passive is also used to emphasise results when the 'doer' is unimportant or unknown. In this sentence, Eighteen websites have been investigated for fraudulent claims, the person who encountered the claims is unimportant.
Another important use of the passive voice is to soften commands. How would a client react if you wrote, Revise the procedures or even Please revise the procedures? This is a strong command to deliver to a client. It would be better to write, The procedures should be revised.
Finally, the passive voice can be used to add variety. This is an extract from an email. After we contacted the supplier and placed your order with them, we arranged for the order to be shipped on 10 July. We then gathered the related documentation from the supplier and shipping company. This was sent to you by courier this morning. The last passive verb sentence changes the pace and therefore, adds variety to the text.
Hope this helps.
Regards
Workplace English Training Expert