Personally I use it to stop certain apps from phoning home or auto-updating, as I manage them with from Homebrew Cask.

There are so many apps which don’t need online access, but still send usage pings or check for updates.

I've read applications like little snitch are popular enough that some malware changes their behavior if it detects it. It must be a non-trivial number. I do personally out of curiosity to see what connections are being made.