Flash filesystem images are useful for storing your programs, extra data, and any other utilities (e.g., qconn, ls, dumper, pidin) that you want to access on your embedded system.
If your system has a flash filesystem image, you should include a devf* driver in your OS image and start the driver in your boot script. While you can mount an OS image filesystem only at the root directory (/), you can specify your own mountpoint (e.g., /myFlashStuff) when you set up your flash image in the IDE. The system recognizes both the .ifs and .efs filesystems simultaneously because the process manager transparently overlays them. To learn more about filesystems, see the Filesystems chapter in the QNX Neutrino System Architecture guide.