Question: Why does the README say it's best practice to not use custom UA or headers?

[SuppliedOrange]

https://github.com/Kaliiiiiiiiii-Vinyzu/patchright-nodejs?tab=readme-ov-file#best-practice----use-chrome-without-fingerprint-injection

Best Practice - use Chrome without Fingerprint Injection
To be completely undetected, use the following configuration:

chromium.launchPersistentContext("...", {
    channel: "chrome",
    headless: false,
    viewport: null,
    // do NOT add custom browser headers or userAgent
});

Why is it best practice to do so? Wouldn't occasionally rotating this to mimic different machines be better?

[Vinyzu]

Because Chrome (or more specifically Chromium) has a bug in which UserAgents do not get applied to WebWorkers. See (for example, i think there multiple but this one was the first one i found) Chromium Bug Tracker.

If you apply a UserAgent, whether via a Command Line Flag or a CDP Command, it can cause a Leak if the Site Checks your Navigator UserAgent against a Webworker UserAgent.
This doesnt mean that there are no cases in which you shouldnt change your UserAgent, it just means that you shouldnt if you want to be completely undetected.