My opinion is if you provide enough places for bacteria to live, it is not needed. Bacteria is everywhere. People need to find a place for bacteria to never be disturbed(bio-wheel, media in the filter such as bio-max, ect.)
Then when you clean your filter floss, you dont have to worry about rinsing it tank water, changing one at a time ect.
For cycling? Well If you seed it right, you shouldn't need it really. But if people want to believe in it, that is fine. I just don't need the expense of another liquid, when it works for me without it.
8)