Color Clusters - how it works?!

Hi,

I have a problem with understanding what color clusters are and how them works. This option is available in some panels like "color range" or "replace color", but I don't know what for and what actually mean "color cluster".

I tried to figure it out through tries and errors but I don't see any differences especially in "replace color" panel. In my opinion it affects in no way to mask creation. 

Can someone explain it to me and maybe link some screens how it change the image selection before and after select "color cluster" in the panel?