I heard from my collegue that in FME and some other ETL tools you will
creating scripts and scripts will create GUI and Mappings and it is
more effecient!

Does Informatica be able to do the same thing?

If yes, how and why we do not usually use it?

If no, what is the reason?

And generally does this make sense? ( Having script and ETL create
mapping and tranformation on the fly? )