Flashing the eMMC resets the MyDocs folder contents to factory settings. N900 users don't need to reflash the eMMC of their device when updating firmware but can do so to clear all data from the device. You may need to do so if you have a pre-production device e.g. in the Maemo Summit. If you have a sales unit and you have problems with your eMMC you should contact Nokia Care. However there are cases known where for instance the desktop widget configuration data which is stored in user's home directory gets corrupted and causes bootloops on hildon desktop startup failing. In this case you'll actually need to reflash your eMMC to recover system from bootlooping (there are other more involved methods to recover too, search for "backupmenu", "watchdogs", "rescueOS")