In games with campaigns level length variation is important for the player engagement. In RPG's the ability to chose quests or side levels when time is short, a player accomplish goals without requiring a major investment of time. This can avoid player frustration with being thrust back into an intense level that was previously started.
Dragon Age: Origins
Dragon age is an RPG that allows the player to select quests that want to work on at that particular time. this allows the player to chose a quest depending on how long they might be interested in playing and elevates the feeling of drudging through a level just to "get to a good spot to save"