Understanding what you have is one thing. Understanding the implications of changing components is quite another.
Like the ripples in a pond, the implications for changing your systems often expands far beyond the point of change. Automated Impact Analysis is an essential pre-requisite for accurate and timely systems maintenance.
Understanding the impact of a change is given by the basic inventory analysis. Legacy Directory shows which programs use which copybooks; which job steps and which jobs invoke the programs; and which data sets are allocated by those job steps. The Legacy Directory automates the task of impact analysis by providing sophisticated searching facilities and the ability to group multiple requests into a single script.
To be truly effective, you need automated impact analysis that is based upon a user-modifiable list of impacted components. This technique means you do not need to know the actual names of data fields in your programs. You decide what kind of processing you need to locate, guess at the name-fragments that are likely to be found in that code and run the analysis. It shows you the lines of code that need to be addressed by your current project.