[glenngillen]

I use Little Snitch to alert on any outbound connections and make a decision. The google stuff immediately got a permanent blackhole for Homebrew. Anything I'm uncertain of I'll give a short-term approval (30mins) to not break anything. After a couple of rounds of execution (and sometimes some trial & error) you can usually work out which requests are essential and which are some notifications/tracking thing.

[daneel_w]

So you didn't see the notice brew(1) gives you on first run?

[glenngillen]

I can't recall, though this approach isn't specific to homebrew. I block it permanently at a network/process level rather than having to remember to set a ENV var.