Growing cannabis from seeds adds an extra stage of the cultivation cycle, as compared to running your plantation on clones. Though a seed contains all that the plant needs for the first few days of growth - similar to an egg - it is always a good idea to help nature in doing its deed.
Seeds from professional breeders tend to have 99% germination rate. In case of older seeds, however, or ones coming from home production, friends and family or some other, less reliable source, it might help to add some enzymes to ensure it a smooth start. In any case, once the seed becomes a seedling, it should be treated with extra care, especially with what concerns the rooting system.
Providing the seedling with rooting enzymes allows the plant to develop a strong and healthy root system at this early stage. It will later become the lifestream of an adult cannabis plant, so in many ways it is a key to large and juicy buds of marijuana. Take care of the seedling and you will have less work with the plant for the rest of its day - healthy roots produce a healthy plant.