Why it is important that to complete documentation?

I can explain the importance of documentation with a simple example below i think it should answer your question.

So consider we have a project to be done we first then start with the documentation specifying the step to step process of what should be done and it goes on like that and the modifications are done accordingly as we move further and complete the documentation successfully. Now any one can understand the project by the documentation as it involves step by step procedure of what is being done in a particular project.

If we don't have the documentation or well maintained documentation and suppose we left the project incomplete and it should be done by somebody else ,due to improper documentation he/she suffers a lot to understand the early stages of the project, so either he/she had to start the project from starting which is a very time taking process or we can say it's waste of time or he/she should make up their so that they understand the documentation to proceed with the project which is i can say impossible.

so the documentation plays a vital/important role for the sucessful completion of a particular project.