The 3D Keyer in DaVinci Resolve was not designed for green screen work, but it can offer a quick solution for simple scenarios. Understanding the keying principle it uses and the role of color spaces in chroma keying helps you get the most out of this tool.
The 3D Keyer was first introduced into Resolve as a 3D Qualifier on the color page. Since v. 17 it is also available as a Resolve FX effect from the edit page. But the keyer’s origins still show through its strentghs: In cases where the HSL qualifier works well (selecting based on Hue, Saturation, Luminance), the 3D keyer tends to work even better.
Though the 3D Keyer is not limited to HSL, the available color spaces are unfortunately not tuned towards green screen or blue screen work. That is the main reason why the Delta Keyer tends to outperform the 3D keyer when evaluating the quality of the keying result.
However, the 3D Keyer does have one main advantage: Speed and ease of use from the edit page. You can use it for simple scenarios that don’t require Fusion, or as a quick way to build previews in the edit. Once you need to work in a more systematic, detailed way, you can switch to Fusion and build an advanced keying solution with Delta Keyer, Clean Plate and more.