From the very top of the linked page:
> Homebrew is provided free of charge and run entirely by volunteers in their spare time.
> As a result, we do not have the resources to do detailed user studies of Homebrew users to decide on how best to design future features and prioritise current work.
> Anonymous analytics allow us to prioritise fixes and features based on how, where and when people use Homebrew
It then goes on to list some examples. Opt in renders this useless.