We work with load tests to ensure that the system is working fine during major campaigns where a significant increase in the number of visitors is expected and also in connection with major system changes. Even minor changes can have major consequences for performance. This is not normally captured in function or regression tests, and it may therefore be a good idea to run load tests continuously in connection with each release as part of the system's QoS (Quality of Service) testing. We also perform stress tests to examine the boundaries and find bottlenecks.
Load tests provide a measure of how well the system works at a given load. To get a fair result, it is important that the load generated against the system really reflects how users move on the site and the tasks they perform. We may need to simulate that items are added to the shopping cart, that users register or log in and that orders are placed. If it is a question of a campaign, the users' behavior can be very different from the normal behavior, the best thing is if you have statistics from previous campaigns that you can start from. The conversion rate is probably higher than on a normal day, so the proportion of users who actually complete the order also needs to be increased in the test case.
We use OctoPerf as a tool for load tests to create user scenarios, generate loads based on the scenarios and then present the results of the load tests. By load testing, you can both get a measure of the system's limitations, as well as valuable information on how to best use your existing resources.