The availability of special purpose simulation languages, at massive computing capabilities at a decreasing cost per operation, and of advances in simulation methodologies have made simulation most widely used and accepted tools in operations research and systems analysis. Circumstances under which simulation is the appropriate tool to use have been discussed below.

• To study the internal interaction among different components of system.

• With the help of simulation system parameters can be adjusted.

• To experiment new design prior to the implementation.

• To verify analytical solution.

• To determine the requirement of system.

• To visualize the plan through animation.

• To observe the effect of environment changes on the system.

• To improve the system through the knowledge gained in designing simulation model.

• To provide better understanding of system operation.

• To perform bottle neck analysis.

• The modern system (factory, service organization, fabrication plant, etc.) is so complex that its internal interactions can be treated only through simulation.

• Changing simulation inputs and observing the resulting outputs can produce valuable insight into which variables are the most important and into how variables interact.

When a system cannot be simulated: There are ten rules for evaluating when simulation is not appropriate.

1. The first rule indicates that simulation should not be used if the problem can be solved by common sense.

2. Simulation should not be used when the problem can be solved analytically.

3. Simulation should not be used if it is easier to perform direct experiments.

4. Simulation should not be used if the cost of simulation exceeds the savings.

5. Simulation should be avoided if resources are not available.

6. Simulation should not be used if time is not available.

7. Simulation takes data, sometimes lots of data. If no data is available, not even estimates, simulation is not advised.

8. This rule concerns the ability to verify and validate the model. If there is not enough time or if the personnel are not available, simulation is not appropriate.

9. If managers have unreasonable expectations, if they ask for too much too soon, or if the power of simulation is overestimated, simulation might not be appropriate.

10. Last, if the system behavior is too complex or can’t be defined, simulation is not appropriate. Human behaviour is sometimes extremely complex to the system.