What is SIP on your Mac and when is it safe to turn it off?

Howard Oakley for Eclectic Light Company:

System Integrity Protection – SIP – is one of the primary mechanisms which macOS uses to protect itself. Introduced relatively recently in El Capitan (2015), you’ll find various recommendations that to fix problems with macOS or even with some apps, you should turn SIP off first. I hope in this article to convince you that it’s never safe to turn it off, and that Catalina makes that even more important with its new read-only system volume…
Before these recent changes to SIP, disabling it was often recommended as a first step when attempting to fix problems in macOS which were blamed on damaged services or Property Lists. I have had a steady succession of advanced users who have turned SIP off and then tried to repair what they thought were corrupted components within macOS. None of them, as far as I recall, was ever successful in tinkering in this way, and every case became rapidly worse once SIP was disabled and they started fiddling around with what should have been protected files…
And if any software vendor suggests that you should run your Mac with SIP disabled so that their software works, don’t trust them in the slightest. Look for an alternative product. Would you trust a mechanic who fixed a problem with your car by disabling the airbags and removing the seatbelts?

MacDailyNews Take: Handy rule of thumb: Don’t turn off SIP unless your name is Craig Federighi and you possess a mane of the Gods.