For a lot of projects that involve huge number of test pages, the immediate advantages of such a feature are:
1) Ability to reuse NameMapping across modules with/without minor customizations.
2) Better organizing of the NameMapping, especially if it involves a huge number of objects.
3) Faster object identification (due to smaller NameMapping modules loaded depending on the feature being tested)
e.g. Modular NameMapping this post is an example of a use case