The coupled atmosphere-ocean GCMs are more useful because they portray more realistically the way the system works. Models have been constantly refined over the years to reflect improved understanding of the climate system. For example, the eruption of Mt. Pinatubo in 1991 caused a noticable dip in global temperature. Scientists already understood in theory the sunshade effect of airborne particles, but in later years it was factored into climate models, and global warming forecasts were revised slightly downward. Models, in effect, are a statement of our understanding of the physical processes that lie behind climate and influence it.
Models are collections of theories so they can t exactly prove theories.
They are smarter than people in the sense that they can do more calculations more quickly. But if the theories and principles underlying the calculations are wrong, then the models too will be wrong. Computer models represent the atmosphere by dividing it into boxes. The boxes might typically be about 150 miles on a side and mile deep spread like tiles across the surface of the earth and stacked a dozen or more high. For every step forward in time, complete calculations are done for each box.