The practical benefit is that you can quickly jump between cross-referenced documents, and also if you change the name of a document, it would be updated where ever that link is used. It has pretty broad use cases in creative or academic settings.
This would be most helpful when using the Outline view
The matter of this being in the Outline view aside, have you had a chance to look at the Document Bookmarks feature yet? It does most of what you describe wanting to do, such that creating a metadata field specifically for holding one single link would be somewhat redundant, or even having a list of links, since there as a whole tab in the inspector for that which includes a built-in editor that reduces the need for navigation in the main editor.
Have a look at §10.3, Project and Document Bookmarks, in the user manual PDF, for the documentation on the feature. For a brief introduction, there is also a section in the interactive tutorial on this.