Stepwise refinement enables the software engineer to concentrate on those "chunks" that are the most relevant at the current phase of development. In other words, concentrate on most relevant aspects and ignore details.
Stepwise refinement was first introduced by Wirth in 1971, applying it to pseudo-code. It can also be applied to flowchart, block diagrams, formal specifications and used in every phase of software development.
You can make mistakes in stepwise refinement. Therefore, you need to check each successive refinement before proceeding to the next level.