You could argue that the subject of this post could be a motto for life, not just for business writing. After all, it’s better to effect things than be affected by them. It gives you more control over your destiny, more flexibility in your choices.
In business writing, it’s also better to be active than passive, especially if you are writing ‘persuasive’ documents like business cases or sales proposals. As an example, look at the previous paragraph. The active ‘voice’ is more powerful at effecting something, whereas the passive voice governs being affected by something.
Try and avoid phrases like ‘the ROI calculation can be found below.’ It sounds stuffy and conservative, but also weak and, well, passive. You’re writing this document, you’re in charge of it, so take control. Better to say ‘The ROI calculation below shows the value of our service to your business.’
The active voice is to do with action, and when it comes to your business writing, it’s action you want your reader to take, otherwise why take the time to write at all?