When a Performance Test?

list itemGet certainty whether the Oracle backend can handle the expected load;
list itemKnow at forehand if the application and database server are not too tightly configured;
list itemDetermine the impact on performance of a configuration change, patch, database migration, etc.;
list itemDetermine the maximum load the Oracle backend can process;
list itemGet insight in the resource usage for future upscaling;
list itemIdentify and solve availability and performance related problems rapidly (outside production hours).