Yeah, @beth_green is right about finding the big stuff fast. But here's an angle I never see mentioned, moisture. If you skip nitrogen and pull a vacuum on a system that's been open, you're sucking all that wet air right into your pump. That trashes your pump oil way faster. So you might save a few minutes on the test but then waste more time changing oil or killing your pump. On a really small, quick repair it might not matter, but if anything was open for more than a minute, that dry nitrogen purge is protecting your tools.