Feature branches in git most frequently only live on the developers machine, often for only a few hours,(unlike feature branches in centralized version control systems, which are almost always long-lived) so there is no harm in not branching if you're only working on something thing . If it is a feature that multiple people need to work on, or needs to be worked on for more than a few hours, then a separate feature branch is of course the correct thing to do.
Branches in git are literally just pointers to commits (write a sha1 object to any file under refs/heads to see what I mean) so they don't really buy you much if you're not frequently switching between locations in the DAG, but can be created retroactively with zero hassle if you do find yourself needing them.
Basically, what you do with your private DAG doesn't matter at all, what is important is that you only publish things that are sensible.
Branches in git are literally just pointers to commits (write a sha1 object to any file under refs/heads to see what I mean) so they don't really buy you much if you're not frequently switching between locations in the DAG, but can be created retroactively with zero hassle if you do find yourself needing them.
Basically, what you do with your private DAG doesn't matter at all, what is important is that you only publish things that are sensible.