Microsimulation is a low-level simulation that shows how objects--such as individual cars on a roadway or airplanes in the sky--react to and affect other objects in the simulation. For example, microsimulation can answer (and model) what happens to traffic if a car slows down. We know intuitively the car behind it must either slow down, switch lanes or crash into the first car. What is not intuitive is this one action's cascading effect down the roadway (for the average driver, the stop and start of traffic with no apparent cause). In this case, microsimulation makes visible (and explains) this real-world annoyance.
Microsimulation is most effectively used in problems that have many interacting objects, like supply chains.