Quick Render allows comp artists to render a part of the scene to see the final result while they work on another part. Once your render sequence is done you can review it locally or send the link of it for someone else to take a pick.
Layer Baker can render high fidelity EXR frame sequences capable of replacing vector assets, like a crowd of characters, for a single bitmap layer, while keeping the link between them for future render updates. It also allows for those baked frames to be retimed, while keeping them updatable still.
Render Layers simplify the circuit from going to Harmony to external applications like After Effects and Nuke, allowing for easy preview, ordering and naming of layers without cluttering the node view with write nodes and unuseful connections.