Which is why you have configuration switches to turn them on and off. The tests ensure that they don't mess with existing features, the switch makes sure the users can't see them.
Lets say person A and person B are working on two features both committing to master.
Person A commits some work to master and pushes to origin. Person B commits some work and pushes to origin. Repeat this a few times, now you want to scrap the feature person A is working on. How do you cleanly handle this?
That said, it seems you are suggesting that the workflow should be centered around rolling back features rather than commits? That being the case, if your feature spans multiple commits, then indeed you have something there. If your feature does not, branching probably isn't needed.
Sure, if you work in some sort of enterprise or corporate environment.