When multiple categorised are "harvested" in Wikidata, Wikidata knows about more items than any of the individual categories. This enables the use of the data in new ways.
- suggest categories based on the presence of statements in the Wikidata category
- suggest statement when an article is included in a category
- include red links in a category when a Wikipedia does not have articles.
Before such functionality will become available, certain tipping points will need to be reached. For instance enough categories need to be harvested in this way and, these categories have to be identifiable for the information they include.
The category "University of Notre Dame alumni" indicates that it is a list of humans AND, for them the statement "alma mater" "University of Notre Dame" has to be made. For over 1450 categories that are about humans similar information exists. Every day more categories are added.
I really wonder what it takes to reach the tipping points that will bring more application of the Wikidata data to for instance Wikipedia.