Yes, they keep your blood sugar levels constant and give you constant energy. Simple carbs is really bad for your body. Eat as many complex carbs as you can, another benefit is that the foods that contain complex carbs often have lots of fiber which is excellent for your digestive track.
Yes, they are the carbs you should always try and eat, simple carbs are not good. 50% of your diet should be carbs, so try and make as many of them as possible to be complex..