The file is a selective, optional component file frequently associated with FitGirl Repacks, specifically designed to enable PlayStation Network (PSN) services or online multiplayer functionality for certain PC games. It is not a necessary file for the base game to function, but rather a tool for accessing specific network features often provided through emulated services (such as those from FreeTP or Héìsenberg).
It is part of the "Selective Download" option. You do not need this file to play the single-player campaign. fg-optional-psn-services.bin