“The ability of the human brain find and process patterns is far superior to any computer. Spiral patterns in disk galaxies are easily seen and followed by people but computer algorithms have a harder time determining where spirals begin and end, especially if they aren’t continuous. That’s where you come in! By tracing the spiral arms you see in galaxy images, you are giving our computer algorithm a boost so it can accurately measure how tightly wrapped the structure is.”
https://www.zooniverse.org/projects/astro-lab-ncmns/spiral-graph/about/research