MioPocket can be installed to SD card or to internal flash disk (SD-free installation). Each has its advantages and disadvantages...
SD advantages: SD cards have ample space, copying to SD card is fastest and returning to factory condition is usually as easy as popping out the SD card and performing a hard reset.
SD disadvantages: using MioPocket requires having an SD card with MioPocket on it in the device at all times and returning from a long standby sometimes requires waiting a few seconds for the SD card to initialize.
Flash advantages: always on the device, so it doesn't require having MioPocket on an SD card or waiting for it to initialize.
Flash disadvantages: requires renaming or editing of original device files (which can be dangerous if the wrong files are changed) and uninstalling MioPocket and returning to factory condition requires changing them back (usually from a computer). Also, North American devices may require removal of a few state maps to make room (see the SD-free instructions for tips on MioPocket components to remove to lessen the impact).