Most people say you do not need to soak legumes before cooking. Unless, we are in a hurry then we usually do not. Personally the yield seems to be larger when you do pre-soak legumes such as lentils. We like to immerse lentils in warm water from the tap with a little bit of baking soda. Cooking time is reduced, therefore you save on energy. Be also sure to drain the lentils and use fresh water for boiling.
By the say, do not leave theme there too long or they will start to ferment. That is another story.