When computing your Web of Trust all follow lists of the people you follow are combined, but someone who follows 100 likely follows less spam accounts than someone who follows 1.000, same for 1.000 vs 10.000. This setting tries to take advantage of that signal. It's not perfect but good enough.

Dunbar refers to https://en.wikipedia.org/wiki/Dunbar%27s_number I didn't know what else to call it. 

 Thanks! Just making sure I understand what it means when I adjust it 😂