Massive speedups once you get to thousands of tests. We 12 minute runs for the 3 apps that are part of a release. When we went parallel it reduced it by 1&#x2F;6 (6 test processes).<p>Of course, we also had some slow tests we rewrote and had to fix some tests that did not play nice concurrently. But it was well worth it.<p>I don&#x27;t think you&#x27;ll see a big benefit for a current 10-second run because of fixed cost of startup is some of that. But running tests in parallel may reveal some bad testing practices: leaving data behind or improper mocking that cause tests to fail in parallel. Fixing all that once you get to a massive set of tests is really painful and slow becuase you have to fix them ALL before switching your testing config. So that might be a benefit to turning it on soon and growing your tests already in an parallel environment.