Researchers often work in silos and continue to create finite focus seeking deeper and deeper explanations for problems. Over time the lens becomes narrow and the knowledge more specialized. There is a constant search to find the head of the pin and few look back to see where their knowledge aligns with other fields. Integrating fields leads to new insights that would not be possible under traditional approaches to research.
Not one explanation fits all situations making theories limited to contingent circumstances. Comparing and integrating theories helps them to be broad based and apply to other industries in a way that a single theory cannot. Together a bundle of theories is more useful and strong than a single unintegrated theory alone.
For example, psychology, sociology and economics are not different fields but different lenses focused on various perspectives of a similar phenomenon. Psychology looks at the individual, sociology at the group, and economics at financial transactions. Together they are able to provide a better explanation of purchasing behavior than what would be possible alone.
Integrating research is a changing of perception as one takes their own theories and compares and contrasts it to other theories. When it fits well with other fields then one can say their work is comprehensively thought out and supported by a wider body of knowledge. The potential application and use of the theory rises.