How do you know whether a database code change is going to be great, okay or awful? If you want to test a new version of SQL Server how do you know whether to leave on or disable the legacy cardinality estimator? Will the latest cumulative update destroy the performance of your application?
You don't have to wait until production to know if the change you are going to do works or not and building a system to test the performance of your database is probably more straightforward than you realize.