Its main advantage over just using COPY or \copy, and over using a Foreign Data Wrapper, is its transaction behaviour, where pgloader will keep a separate file of rejected data, but continue trying to copy good data in your database.
The default PostgreSQL behaviour is transactional, which means that any erroneous line in the input data (file or remote database) will stop the entire bulk load for the table.
pgloader also implements data reformatting, a typical example of that being the transformation of MySQL datestamps 0000-00-00 and 0000-00-00 00:00:00 to PostgreSQL NULL value (because our calendar never had a year zero).
Repository: https://github.com/dimitri/pgloader
License: The PostgreSQL License