Camera's have an LCD screen since it makes it easier to frame a shot. But there are times when the glare from the sun makes it difficult to compose pictures from the screen.
It is in times like this that the advantages of the viewfinder shine through. Additionally, when you frame a shot with the help of a viewfinder, you can hold the camera more steadily in addition to preventing an accidental camera shake and blurry pictures. It works well for a zoomed it shot as well, making sure that the shot remains stable. Lastly, when you take a photo using a viewfinder, you also save battery power.