Well, that's a relief. I run an average of 4-5 brew commands every minute, so at least there's that. /s

> when you run `brew install` or `brew upgrade`

So, only the two most used `brew` commands (for me, at least) will trigger a series of git fetches and merges over the network and an in-place update of the code.

> You can [...] disable this functionality with `HOMEBREW_NO_AUTO_UPDATE`

Why was it enabled automatically in the first place? Why wasn't I notified when homebrew updated that this was the new default behavior. Why must I always dive into homebrew on github to identify (1) why it's not behaving the way I would expect a package manager to and (2) how to get back sane package manager behavior?

If there's been no updates there will be no `git fetch` run. We use a newish GitHub API to check for updates as its quicker.

> Why was it enabled automatically in the first place?

A significant numbers of our created issues are due to people having failures when they don't run `brew update`. This solves that.

> Why must I always dive into homebrew on github to identify (1) why it's not behaving the way I would expect a package manager to and (2) how to get back sane package manager behavior?

We're an open-source project run by volunteers for free in our spare time. We're underfunded and understaffed so our communication is lacking. The best current place to find out about such things is to follow our issue tracker. We aim to improve this in future.