Balance is a design principle relating to the visual weight in the frame. An empty image with just a single subject on one side of the frame would be heavy towards one side. This image of a bird on an empty background shows that well.

The Principles of Design in Photography - Balance

This image of a fishing pier and its reflection on the lake show an image perfectly balanced over a one of the thirds in the frame. Placing areas of interest over a line or cross section that is one-third in to the frame is an excellent compositional rule.

The Principles of Design in Photography - Balance

While it can’t be said whether a balanced or unbalanced image is good or bad compositionally, balance should be used purposefully to achieve what you are trying to do.

Be sure to browse around some my images on the site that are for sale and find balanced or unbalanced compositions!