i assume they are talking about using your mouse scroll inbetween the right and left buttons? If you zoom in far enough i believe it turns it first person.
I've tried it, coming from an FPS background. It's kind of interesting, but in a game like this, not very practical when you need a good overall view of your enviroment.
A nice feature that comes with the first person mode is that your view is not as severely restricted in vertical panning as it is in the third person mode.
You may find that you are unable to look at the top of that tall statue in the 3PV because the floating camera is blocked by the scenery behind you. Switch to 1PV and you can look almost straight up and straight down.
But, as has been said by the previous posters, 1PV is not really useful in action. You need the environmental awareness supplied by the 3PV. I use it strictly for sightseeing when I'm on one of my journeys to forgotten explorables.