Purpose of Load Test

What is the purpose of a Load Test?
The purpose of any load test should be clearly understood and documented. A load test usually fits into one of the following categories:
Quantification of risk. - Determine, through formal testing, the likelihood that system performance will meet the formal stated performance expectations of stakeholders, such as response tme requirements under given levels of load. This is a traditional Quality Assurance (QA) type test. Note that load testing does not mitigate risk directly, but through identification and quantification of risk, presents tuning opportunities and an impetus for remediation that will mitigate risk.
Determination of minimum configuration. - Determine, through formal testing, the minimum configuration that will allow the system to meet the formal stated performance expectations of stakeholders - so that extraneous hardware, software and the associated cost of ownership can be minimized. This is a Business Technology Optimization (BTO) type test.

Load Testing

Why is load testing important ?
Load Testing increases the uptime for critical web applications by helping you spot the bottlenecks in the system under large user stress scenarios before they happen in a production environment
When should load testing be done?
Load testing should be done when the probable cost of the load test is likely less than the cost of a failed application deployment.
Thus a load testing is accomplished by stressing the real application under simulated load provided by virtual users.