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To be clear, this is an informative post, not a request for advice. We've already started doing things this way.
The master branch of the vanillaforums repository will always contain our latest production (release) code. It should be the most stable source code you can download from us, but also the oldest. New code only gets into master when we release a new version or create a hotfix.
All of our unreleased development work ends up in the develop branch. Sometimes it is committed directly, other times it comes from merged hotfixes again a release, and other times it comes from a merged feature branch. This branch will always contain the most bleeding edge vanillaforums code, so it sometimes has bugs and unfinished features. Use this at your own risk, and avoid deploying it in production.
When we're getting ready to tag a release as a beta, we'll branch develop into release. This allows us to feature-freeze the code and more easily commit bug fixes without having to tediously create hotfix branches for every little thing. This code should be of beta or rc quality, for the most part, and is what you should download if you'd like to help us test.
Feature branches are work-in-progress branches that contain large chunks of new or modified code for a single feature or refactoring task. They are branched to preserve the stability of the develop branch during fairly destructive code changes.
Hotfixes are branched from master and exist to fix small bugs that are detected in a release after it has been tagged in master. These branches are usually small and concise, and are merged back into master and develop once they are completed. They should never be new features.