The most effective strategy is to cache DataFrames that are reused multiple times. Caching the initial raw data before any transformations might not be beneficial if the transformations significantly reduce the data size. Caching every intermediate DataFrame, even those used only once, adds unnecessary overhead. Avoiding entirely is not optimal, as caching can significantly improve performance when used strategically. Caching only the final DataFrame is useful if the entire feature engineering process needs to be reused, but it doesn't optimize the individual steps within the process. Caching is most useful at points where derived data sets (i.e. after heavy calculations) are used repeatedly.