Once you are done with your research and dissertation and have achieved your doctorate, you will start looking for jobs that match your qualification. You may also choose to study further in your field and opt for joining an institute as a student. Whatever you choose to do, you will be asked to do a post-doctoral research. Here is a list of people who have to do post-doctoral research:
If you are seeking a temporary role in an academic position: Such a pursuit will require you to do a research within your field to be able to prove yourself worthy of the position. The research will be evaluated to check whether you fit the role and whether you may be able to add value to the job.
If you seek to join an institute as a faculty in the subject: You may have the expertise and the confidence, but the people that hire faculty for institutes, require more than that. You will be asked to do a research in your field of interest even after having completed your doctorate, if you want to join as a faculty.
If you want to earn a higher degree: In a whole lot of countries, you post-doctoral research may earn you a qualification that is a step higher than the doctorate that you already have. If you need to keep your drive for learning alive, you need to do a post-doctoral research.
If you want to get published: When you need to have yourself published in famous journals and reading materials, you need to do a research even after you finish your doctorate.
The prospect of having to carry out a research all over again may be a daunting one, but it makes sense to keep going if you need to reach great heights.