This feature needs to be in the game for immersion reasons. After all, we are speaking about a role-playing game. Dialogues, choices, quests, living cities - it's all awesome, but you gotta be able to blend in with the world. However, simply switching between walk and run doesn't cut it because your usual walking is often too slow to actually get to places, even within towns. And sprinting around towns and cities makes the character look like an idiot. Therefore, just like gamepad / console players can adjust the speed, PC controls need to have this ability too.