They explain the obvious. Avoid such theories when writing to professors. If your theory does not tell your audience anything new, find another theory. Some theories are not internally consistent. If parts of your theory contradict each other, find another theory or adjust your theory to eliminate the contradictions.
Some theories are very technical.
All theories are partial or limited, some much more than others. In short, all theories leak. You must use any theory appropriately. Do not apply a limited theory to something it does not map onto well. Do not overgeneralize a theory.