The talk was divided into two parts: the first part was about a custom binary serialization created to serialize complex pandas data frames that did not fit well with conventional serialization methods. The second part was about optimizing JSON serialization of thousands of data classes with nested lists and models. The speaker explained the challenges of deserializing and serializing back the data and how they solved it. They emphasized the importance of knowing the tools and the internals to write more performant code and advised caution when going low level and breaking the rules without a proper architecture.