A simulation model is a virtual copy of a real system. Particularly, with a simulation model you can analyze systems' dynamic behaviour while understanding disturbance effects and volatility.
Simulation is a crucial tool to support decision-making. This can be used to perform what-if analysis as well as it can be coupled with optimization tools (e.g. black box optimization).
Spotting and aligning errors, exploring new ideas in a “off-line” simulation environment do cost 10-100 times less than in a on-line environment.