The CoGroupByKey transform is a fundamental Beam operation that combines multiple PCollection objects, grouping elements by a common key. Unlike SideInputs, which require the entire dataset to be available to each worker, CoGroupByKey efficiently distributes data across workers through a shuffle operation. This method is particularly beneficial for large datasets that exceed worker memory capacity. For optimal performance when dealing with extensive datasets, CoGroupByKey is recommended over SideInputs. Reference: Building Production-Ready Data Pipelines Using Dataflow