> you couldn't change something and test it on a whim
You could. It would just not leave your branch for a while. Around the scheduled merges it would run against the tests of progressively more of the larger organization.
Parts of this actually constituted a good way to prevent being distracted by the bugs of faraway teams. If something reached your branch, where you were working, it was vetted by the tests required to make it into winmain.
The downside was that people got fairly political about what goes into the branch and when, even for small things.