Possible consequences of forced shut down
At boot time a file consistency check is performed, usually a quick check to see if the filesystem was unmounted cleanly. If the filesystem is dirty (not unmounted cleanly) then some form of fsck is performed. fsck attempts to fix filesystem metadata not a files actual data. So, there is always the potential for data loss. fsck will not fix some inconsistencies and at some point a filesystem can become inconsistent and cannot be repaired. So, it is best to avoid hard shutdowns though the filesystem is not fragile.