You should look at the beauty of fractals! http://en.wikipedia.org/wiki/Fractals Also, the golden ratio was the height to width ratio of most canvasses. Golden ratio: (sqrt(5)+1)/2, aka 1.6180339...
Art can be used for:
Expressing peoples feelings
Fame
Money
School work
Illustrating a veiw
These are just a few ways art can be used for.
Different artists have different reasons.