"It looked like this yesterday" is a hard thing to act on. A capture is how you stop saying it. Efflux renders the URL and keeps what came back: the screenshot, the rendered HTML, the cookies, the headers, and the network log.
Show the page instead of describing it
When you are explaining a finding to someone who was not there, a capture does the explaining for you. Engineering sees the same response you saw. Legal sees the same banner. Nobody has to trust your retelling, and nobody has to hit the target again to check.
That matters most when the page is going to change. A misconfigured redirect, a third-party script that should not be there, a cookie set without the flags you expected: all of it is gone the next time someone deploys.
Look at what the page loaded, not just what it showed
The network log and the cookie report are often more useful than the screenshot. You can see which third parties the page called, what it set in the browser, and what the headers said. That is usually where the answer is when a page looks fine and behaves badly.
See it from where your users are
A site can serve different content depending on where the request comes from. Pick a region, country, or territory and the capture renders from there, so you can compare what two audiences actually receive.
Where to go next
Captures covers the request, the regions, and the artifact routes. If you are capturing on a schedule or in bulk, attach a callback so you hear when each render is done.