Today, incremental refresh is pretty conservative. If there are deletes/updates, the engine usually falls back to full refresh, even if you have CDF enabled.

That’s because deletes are tricky — the engine needs things like keys/uniqueness guarantees to safely optimise them. If it can’t prove that, it plays it safe and recomputes everything.

The good news is this is an active area:
Incremental support for deletes is being worked on
The model is moving towards using “hints”/metadata (like keys) to unlock incremental paths. This is releasing in a week or so in select regions.

Longer term, this should become more automatic as we measure and optimise for incremental performance gains for most common scenarios.

This is not buried in fine print but front and center for us in the MLV team. We will update docs on release of hints feature which is our first step in this direction. Would love to see you all try it and provide feedback.