Importance: Focal length is the most important feature that affects an image. it controls the angle of view through which we can select that how much scene of picture we need to select before taking a photograph. Moreover we can say that it also gives us an idea that how much the subject will be magnified for a given photographic position.
Increasing the focal length will allow us to take a picture of the same scene thus capturing the more details of a smaller part of the scene in front of us. More focal length will enable us to take picture of some specific subject on a distance without making the picture blur.
Example: We are at a distance of a Lake with a boat and it is surrounded by the mountains. If we want to focus the boat than with more focal length it will be possible to take a quality image.
Conclusion: The More the Focal length is the better wider pictures in can take from a distance as well.