Side lunges are a great exercise for working on your lateral quickness and flexibility. It is not a complicated basketball exercise, but it is great for developing strength in the legs and flexibility. The key to being able to move quickly and explosively laterally, is opening up the hips and developing good footwork. In order to make the moves that you need to make, you are going to need to be low and in an athletic stance. However, if you are not able to get low because your hips and core are tight, you have a problem.
One area that directly relates to this exercise is, on the ball defense. As a player you must be able to slide your feet and keep your man in front of you, otherwise they are going to get an angle to the basket and put your team in a bad situation. If this happens enough times it will most likely result in the player having to sit the bench. So along with working on defensive basketball drills, make sure that you are also working your leg strength and flexibility.