The output of the sample filter allows artists to (mostly) automatically generate IDs for use in a compositing package such as Nuke for selecting and masking operations to specific objects or material selections. You will find example files in the Katana and Maya pages on Cryptomatte output. Below are object and material results of Cryptomatte output on a simple scene with a teapot.
The file name of the EXR image to write to, the default is “cryptomatte.exr”. For now this is (required) written to a separate file from your beauty or denoise EXR output.