When it is time to get things done, you do not want to have to go anywhere but your lists to find what to do.

If it is stuck in a Project Plan, then you will have more places to search for things to do. Chances are, you won't.

Keep a list of Next Actions and use that.

If you are a pen and paper-only person, then you may have a Project Plan in your project folder, for example, but the Next Actions will be on your Next Actions lists... which you want available to you wherever and whenever you will be in a position to do anything on them.