The slides make reference to ELT rather than ETL.... ELT is for "schema on read" whereas ETL is for "schema on write" solutions. ELT is more suitable for "file system based" Data Lakes (object storage in AWS S3) while ETL and ELTL is suitable for relational database data warehouse environments (Redshift). ETL is meant to be done by a separate middle ware service between the source and the Redshift Data Warehouse, whereas ELTL is meant to be done entirely in the Redshift Data Warehouse. ELTL is the preferred and modern way method of working in an MPP DW environemnt.