The Phantom 3 and 4 had very wide angle lenses like a gopro - these are able to focus acceptably from a few feet away to infinity without any manual or automated adjustment.
The field of view is a bit narrower on the Mavic camera - things look closer, more like how we would see them.
To focus correctly close to the camera as well as out to infinity there is now a need to adjust the focus by tapping the screen over a near or distant subject in frame.

The thing to watch is that usually when you start up it has fixed on something fairly close by and then distant things are going to look soft a you get higher.
On the back of the controller are two (customisable) function buttons and one by default is set to re-focus on centre of the frame - which is a quick way to do it, and will be useful if sun glare is making it hard to see properly. 

I think once you've flown it a few times this will seem natural enough but some early reviewers weren't aware of it and had some awful mushy soft results. 
In most cases once you see it focus where required it won't need tapping again during the flight.