Protective glass for iPhone Xr is important because it gives you a second chance if you lose your iPhone on the floor. 

Normal protective glasses don't go download to the edge of your iPhone because they can't be bent as much as Apple bends the glass on an iPhone, but that's where the 3d protective glass comes in, it does all the way around the edge of your iPhone's glass so it doesn't just protect the glass but also the corners and edges with an aluminium frame that is made to hold a little of each.

iPhone Xr has a screen that goes to the edge of the iPhone, it has the same design as the other newer iPhones almost, but it has a little more edge than the more expensive iPhones therefore a metal edge is the obvious solution to protect the edges of your iPhone screen. Aluminum holds better than glass and it's the edges of an iPhone Xr screen that get exposed the most because it's the ones you usually lose your iPhone on and that's also where the power of a loss or shock has at least glass of benefits to That's why the edges and corners are both most exposed and also easiest to smash when you drop your iPhone. 

This protective glass can be used with a cover, so your iPhone Xr is protected all around.