A long running branch is usually a feature branch that is worked on over a long period of time. Just committing everything to master is asking for trouble.
If everyone works in master, you try it, run the tests, and if they're green, you know it works for everybody. You don't risk breaking feature branch X that did a refactoring in a different direction in an overlapping area.
Of course, this implies that you adhere to a CD/CI philosophy. Code always compiles, all test always pass. If your process involves code being uncompilable, unintegrable or test breaking for substantial periods of time, you'll need branching.
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.