Contouring essentially to casts 'shadow' on parts of your face and vice versa with highlighting. There are areas of the face that light should be on as well as shadow cast, this ensures the facial features are emphasized and played up.
Highlighting and contouring properly also ensures the face comes off chiseled and defined even when the facial features are not as unique. It's important to perfect highlighting and contouring in super easy steps especially if it's desired for everyday wear, which can be done light or heavy for different occasions.
Though the highlighting and contouring trend sees to casting light and shadow on appropriate areas of the face, it should be done well to achieve the desired effect.