microbes are good for nutrient uptake, disease suppression, plant immune system helper, do a multitude of things for soil health

this guy can give a quick rundown on it
Microbe Organics


if you want some real knowledge about microbes look into
dr elaine ingham(probibly top soil biologist in world) Soil Foodweb, Inc.
jeff lowenfelds does alot of work off of dr ingham, lowenfelds has a cheap great read on microbes teaming with microbes