Symmetry vs. Asymmetry
There are two ways of creating balance in a composition.
Symmetrical designs place identical or similar objects on either side of a center axis. These designs are formal, classic, and stable.
In asymmetrical compositions, the axis is often off center or diagonal. Objects of varying visual weight are placed in such a way that the overall composition is balanced. Asymmetrical designs are more dynamic.
The first is a symmetrical cover design, the second an asymmetrical design. Notice how your eye stays in the center of the first cover, and is led to the right in the second cover.