Whether you need to side chain depends on several things, there are no set rules about it, personally I always side chain, because I like the pumping sound you get as the kick and sub rumble along, but also for technical reasons, ducking the sub (thats the technical term) by side-chaining the kick, means that you have maximum headroom for the kick, rather than having it fight with the sub for volume
Try it for yourself, setup a simple sine wave synth, low frequency sub style, no harmonics, and play it as a continuous note...then try playing a kick over the top, compare the sound of the kick when played without the sub, you will hear that the kick is weak, you may even notice that the sound as a whole becomes muddy.
I like big fat kicks, not all of drum and bass is made with kicks in this style, but as already said, the more harmonics you have, and the more crossover you have between the kick and sub, the more you need to either side-chain, or EQ; over doing EQ can kill the sound, side-chain allows for a richer sound, without worrying about headroom in the bottom end