With a temp save, if you die, you cannot start over again (meaning turning the game off and then back on again if you screw up, that save is gone forever.) the way you were when you loaded up the temp save. Say you were wearing a Koopa shell when you orginally did the temp save, but not when you previously did a hard save. If you die, you lose that koopa shell and cannot reboot and get that shell back. The temp save was where you had the koopa shell, and now the only way to get it again is find it in a level, and complete the level, because if you stop mid-level and exit via the pause screen, you go back to the map as you were when you went into the level.