This node can give you a quick one-node solution to getting all of the passes you want combined while only using one node to do it. If not denoising, working with render passes can get messy fast.
Mind you, my observations are not scientific, but feel free to compare for yourself. When using this node, each pass lighting pass also uses that pass's color data as the denoising albedo, which should contribute to better results for that particular pass. This is especially true when working with volumetrics, which consistently muck up the other passes when denoised as one. In the case of denoising, I've found that denoising each pass separately provides more consistent results, with less denoising artifacts. There is also the option to disable denoising if that isn't your thing, so that this can be used as a quick and dirty pass combiner node.
All passes are combined using the same methods as Blender does internally, except where documentation was unavailable. Each pass - diffuse, gloss, subsurface, etc - are denoised separately and have faction options so that you can output only the passes you want to use. It handles each render pass separately, and makes it easier for you to pull out the passes you want to work with. So Blender's compositor denoiser is pretty swell, but sometimes you want a bit more control over the end results.