Flash filesystem images are useful for storing your programs, extra data, and any other utilities (e.g. qconn, ls, dumper, and 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 image filesystem only at /, you can specify your own mountpoint (e.g. /myFlashStuff) when you set up your .efs 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.