Key Mapping
Customizing for key mapping under is recommended but not mandatory. You can use key mapping instantly, without doing any Customizing.
The use cases for Customizing key mapping are as follows:
Changing Default Key Mapping Settings
Extending Key Mapping Settings for Existing Business Objects
Typically, you extend existing key mapping settings by adding new object IDs.
Extending Key Mapping Settings for New Business Objects
The Customizing activities you use to extend key mapping do not enable key mapping. After you define elements such as object IDs, you must implement them in code. You can refer to the code for existing key mapping entries to implement new key mapping entries.