One problem I’ve seen is that most non-trivial apps have both OLTP and OLAP elements in the same places. Think of how many “mini-dashboards” you see sprinkled t

One problem I’ve seen is that most non-trivial apps have both OLTP and OLAP elements in the same places. Think of how many “mini-dashboards” you see sprinkled throughout the UI of a modern CRM. ORMs are generally not good at or even capable of efficient set-based operations spanning entitles. Building a dashboard with an ORM results in pain and wildly oversized DB instances in my experience.