One other beneficial side effects of having an automated test suite is that they come in handy during any profiling one need to do against the code base. Trigger the automated test suite from the profiler and analyze its output to any performance bottlenecks in the codebase.

Also the practice and triggering the of automated tests regularly (continuous integration) and tracking the time it takes for the tests to run helps to detect early in the development cycle if any of the changes made were suboptimal. All environmental factors being equal a new small feature implemented shouldn't drastically increase the time it takes to run the test suite.