Benefits of Compost Tea
The benefits of compost tea can vary widely and they depend upon the ingredients of each batch which can also vary. While completing my degree in Horticulture I have been privy to some of the science behind compost tea, soils and plant health.
I do not profess to be an expert in any of these fields, but it does seem likely from my research that a greater diversity of microorganisms in the soil and surrounding plant life is beneficial. The microorganisms help to aggregate and form soil into a structure that is conducive to plant growth. They break down minerals and make them available, or more readily available, to the plants. These organisms may form a barrier against pathogens, or out-compete pathogens thus reducing the amounts and species of pathogens that might harm the plant.
If you are interested in further research or information, I suggest you start with the Soil Foodweb site, the USDA's Soil Biology Primer or the many university affiliated extension sites that will give you the basic background information.