You can optimise your schema to suit your application code, or you can optimise your schema to fit your domain model. Doing the former makes your glue code easier. Doing the latter gives you maximum performance and the maximum querying power of your database engine.

You can optimise your schema for the convenience of your application code, or you can optimise it for the truth of your domain model. The former makes glue code easier. The latter gives you stronger constraints, better performance, richer queries, and a database that can answer questions the application code never anticipated.