To go back to the sources is the basis of all research. In fact, what separates good research from bad research is just this. Let me give you two reasons why this is so.
First, it is possible that the secondary research did not do a good job at looking at the original sources. At times original sources are in foreign languages and there could be mistranslations and various errors. Hence, it is essential to look at the original sources for yourself.
Second, even if all secondary research is based on solid research, the thoughts of scholars are all based on interpretations and biases. Hence, by reading the sources for yourself enables you to have your own voice and opinion.
Third, by looking at the original sources, you may find new things. All people come to research with different question and so they find different things.