While exploring Xcode9 Beta Found Safe Area on Interface builders View hierarchy viewer. Got curious and tried to know about Safe Area on A
The Safe Area Layout Guide helps avoid underlapping System UI elements when positioning content and controls.
The Safe Area is the area in between System UI elements which are Status Bar, Navigation Bar and Tool Bar or Tab Bar. So when you add a Status bar to your app, the Safe Area shrink. When you add a Navigation Bar to your app, the Safe Area shrinks again.
On the iPhone X, the Safe Area provides additional inset from the top and bottom screen edges in portrait even when no bar is shown. In landscape, the Safe Area is inset from the sides of the screens and the home indicator.
This is taken from Apple's video Designing for iPhone X where they also visualize how different elements affect the Safe Area.