There are different ways to transfer data between database and .gpn files. If you click on "Save in database", the entire .gpn file is exported to the database, any modifications of the database carried out in the meantime are overwritten.
Sometimes the timetable scheduler would like to continue with his/her work offline and would like to transfer only the changed data set to the database, because during this time, his/her colleagues are working on the database, as well. The necessary functionality provides "Merge in database".
Data can certainly be exported any time from the database to a .gpn file .