You can explain so much more diagrammatically and as an image, than can be explained through words alone. This means the ideas which you are wishing to express are effectively leveraged and more clearly expressed.
Reality is a series of images and experiences. To therefore see our goal as an image as opposed to words allows us to more readily connect with its achievement in reality. Also, true reality has its foundation through and behind our mind. Therefore seeing a mental image is allowing it to connect with true reality, and charges it with its secret powers.
What we see around us is images in the present. An image in our mind can be put forward into the future. This therefore allows us to see that image in relation to things which have yet to come about in our lives.
Visualisation is like a sense that does not need to be taught. It is a natural ability that allows us to achieve our goals easily and with very little effort on our part. The secret is to use it in concentrated and particular times of the day only, so that we are constantly kept on the right mental track.