The current RA behavior of allowing per-core/per-directory/per-game configs probably works for most use cases. However, there are uses for having customized playlists, and the existence of playlists could allow for some fine customizations without being coupled to file tree structure.
For example, a user might want to use custom playlists to separate regional variants of the same system, but it may prohibitive to reorganize the content. In another example, a user might have a NAS with all their files and access the files with a computer and another system like a custom arcade cabinet and may have a need to organize them differently without changing the underlying structure.
The playlist could be used as a differentiator for different settings, similar to how content directory is used now. Would anyone be interested in this enhancement?