Quote Originally Posted by Revanche21
doesn't say too much about benefiting plants immediately, seems more like a long-term thing

like if you were to use the same soil over and over
Umm I thought it was pretty clear.

I cut out the important parts and put them in this quote:

n the carbon cycle, microorganisms transform plant and animal residues into carbon dioxide and the soil organic matter known as humus. Humus improves the water-holding capacity of soil, supplies plant nutrients, and contributes to soil aggregation. Microorganisms may also directly affect soil aggregation. The extent of soil aggregation determines the workability or tilth of the soil. A soil with good tilth is suitable for plant growth because it is permeable to water, air, and roots. See also Humus.

Soil microorganisms play key roles in the nitrogen cycle. The atmosphere is approximately 80% nitrogen gas (N2), a form of nitrogen that is available to plants only when it is transformed to ammonia (NH3) by either soil bacteria (N2 fixation) or by humans (manufacture of fertilizers). Soil bacteria also mediate denitrification, which returns nitrogen to the atmosphere by transforming NO3− to N2 or nitrous oxide (N2O) gas. Microorganisms are crucial to the cycling of sulfur, phosphorus, iron, and many micronutrient trace elements.

The region of soil surrounding plant roots, the rhizosphere, may contain beneficial microorganisms which protect the plant root from pathogens or supply stimulating growth factors. The interactions between plant roots and soil microorganisms is an area of active research in soil microbiology.
So the sooner you introduce the micro-organisms then the sooner they are by the root system and the healthier plant you'll have. They help increase the quality tilth, help cycle many important nutrients/micronutrients and protect the plant root system from pathogens and stimulates growth. It's not like this is going to increase your yield by 50% or anything. It's more or less to ensure you have a strong robust plant.