Good q. For most standalone vector search use cases, FAISS or a library like it is good.
However, FAISS is not a database. It can store metadata alongside vectors, but it doesn't have things you'd want in your app db like ACID compliance, non-vector indexing, and proper backup/recovery mechanisms. You're basically giving up all the DBMS capabilities.
For new RAG and search apps, many teams prefer just using a single app db with vector search capabilities included (Postgres, Mongo, MySQL etc) vs managing an app db and a separate vector db.
However, FAISS is not a database. It can store metadata alongside vectors, but it doesn't have things you'd want in your app db like ACID compliance, non-vector indexing, and proper backup/recovery mechanisms. You're basically giving up all the DBMS capabilities.
For new RAG and search apps, many teams prefer just using a single app db with vector search capabilities included (Postgres, Mongo, MySQL etc) vs managing an app db and a separate vector db.