"Checkpoints are snapshots that save the state of the image as the renderer works on it. While view-able as ordinary images, these are also slightly larger than usual because they embed extra state that the renderer needs in order to recover the render. If the render is interrupted or fails for some reason, the renderer can resume the render from the last checkpoint image. If instead, the render finishes then the extra state will be removed when writing the final version of the image."
I know that Arnold currently doesn't support it, but is this something that could be added as a feature?