ETL - The process of extracting data from multiple sources.(ex. flat files,XML, COBOL, SAP etc) is more simpler with the help of tools.

Manual - Loading the data other than flat files and oracle table need more effort.

ETL - High and clear visibilty of logic.

Manual - complex and not so user friendly visibilty of logic.

ETL - Contains Meta data and changes can be done easily.

Manual - No Meta data concept and changes needs more effort.

ETL- Error hadling,log summary and load progess makes life easier for developer and maintainer.

Manual - need maximum effort from maintainance point of view.

ETL - Can handle Historic data very well.

Manual - as data grows the processing time degrads.

These are some differences b/w manual and ETL developement.