The iPhone camera is quite versatile in its photo taking capabilities. I do not use the Portrait mode very much, but it does come in handy at times. One helpful feature of Portrait mode is the ability to do some depth of field editing of the image in the photos App. Here is how that works.
An image that is truly in Portrait mode will show this indicator in the Photos App.
When you take this photo into the editing mode, you will see this addition to the list of available Adjustments.
When you expand the Portrait editing area, you get this one adjustment.
This is basically a Depth of Field adjustment for the photo.
Moving the slider to the right reveals more of the foreground and background of the photo.
Compare this adjustment to the original portrait rendering at the beginning of this article.
The portrait mode is a nice feature for taking certain types of photos. It is helpful to be able to adjust the Depth of Field blurring effect in the Photos App because you do not have that much control over that during the photo taking process.