Monochrome workflows have a special place in my heart. They've saved me from some really tough element-removal work. From markers, reflections, flares, edge treatment and even cosmetic issues.
By combining your R, G, B channels in unique and interesting ways, you can completely cancel out some problems that would be fairly manual otherwise, into a single monochromatic channel that can then be the foundation for replacements of those problem regions.
You can download the tool here
Here's a digestible breakdown of relative luminance