When added to soil or coco, the Mycorrhizal fungi forms a symbiotic relationship with the roots; breaking down elements and making them available to the plants whilst feeding on the carbs that the plants produce. Think of them as a root extension, increasing nutrient uptake and speed of development.
Micro organisms form a barrier against fungal pathogens such as fusarium and pythium, whilst bio-stimulants balance and co-ordinate biological activity. Use at every stage of potting up. This is rocket fuel for soil and coco mediums!