The tools available for working with source code are richer and more mature than the tools available for working with designs.
This group of tools relates to editing source code.
Some programmers estimate that they spend as much as 40 percent of their time editing source code (Parikh 1986, Ratliff 1987). If that's the case, spending a few extra dollars for the best possible IDE is a good investment.
In addition to basic word-processing functions, good IDEs offer these features:
Compilation and error detection from within the editor
Integration with source-code control, build, test, and ...