I think that being able to assess your own work can be a very useful skill to have. If you are able to assess your work before turning it in you might be able to find little mistakes you made or find a better answer than the one that you put down. You would be able to make the things that you do better. Generally, you would be able to improve your work in areas that you need help in by yourself. If you are doing a job you could impress your boss by doing better than they expected you to do.