What are the engineering trade-offs here? Metric were migrating from CouchDB, so using a JSON field is the obvious solution, but what about for new projects?

Compare it to say, Django-CMS, which achieves pretty much the same thing by storing the tree data-structure directly in SQL. The `django-mptt` library handles the details of efficiently implementing a tree structure in SQL, and `south` simplifies database scheme migration. As a programmer, which system would you rather work with?