What is the importance of documentation?

What is the importance of documentation ? And also what is good documentations techniques.

Documentation is very important. Work done at each phase is required in the next phase. For example, requirements are mapped in design so work done at requirement phase is required in design phase. Design is required to convert into implementation. Best way to convey previous work done is through documentation. So at one hand, documentation is required for well managed development. On the other, it is required for later maintainenace. When system is in use, some problem occurs, maintenance team requires documentation to identify exact place of problem as well as for measuring the impact of change on other parts.

This is the reason that why documentation is needed to be focused. There is no specific technique for documentation. Documentation is done in parallel with development. At every stage, everything is documented. For example, in requirement phase, SRS and FRS are developed. In design phase, design document is developed containing every model. In testing phase, test-cases are written. Document of a project is collection of all these documents. They are merged into a single document to provide complete information about system.