Ah, the age-old debate! It really boils down to a trade-off between upfront cost and downstream flexibility. Here’s a glimpse into what I’ve observed works for different teams:

Early Transformation (ETL Focus):

Pros:

-Clean and Fast Models: Models receive pre-processed, analysis-ready data, leading to faster training and potentially simpler model architectures.

-Reduced Redundancy: Transformations are defined and executed once, avoiding repetition across multiple models.

-Improved Data Governance: A centralized ETL process can enforce data quality standards and consistency.

-Resource Optimization: Heavy lifting is done in dedicated infrastructure optimized for ETL.

Cons:

-Reduced Flexibility: Changes to transformations require modifying the ETL pipeline, which can be time-consuming and impact all downstream processes.

-Potential for Information Loss: Aggregations or filtering done too early might discard information that could be useful for specific modeling tasks later.

-“One-Size-Fits-All” Challenge: Transformations might not be optimal for every modeling objective.

Deferred Transformation (ELT/Modeling Focus):

Pros:

-Maximum Flexibility: Data scientists have more control over feature engineering and can tailor transformations to specific model requirements.

-Faster Iteration: Experimenting with different transformations is quicker as it’s contained within the modeling workflow.

-Preservation of Granularity: Raw data is kept longer, allowing for more diverse analyses and future use cases.

Cons:

-Computational Burden on Modeling Infrastructure: Training can become slower and more resource-intensive with complex, on-the-fly transformations.

-Potential for Inconsistency: Different teams or individuals might implement the same transformations in slightly different ways.

-Increased Complexity: Managing transformations within multiple modeling pipelines can become challenging.