You don't need to illustrate before and after. You also don't need the devlog to be detailed either. However, the more details the better. The devlog is just an outline of your work for you to keep track of your updates and for the community to know what you worked on. It is true most people won't read the devlog but it is still there for information on the work you did to improve your project. Put a little work into it. It helps as good documentation of your progress or failures.