How to configure Stub Cost Num?

Hi, I noticed this in the User's Guide: stub cost num No external (except default) routes are flooded into stub areas. Setting this value marks area stub with defined cost of default route. Default value is no. (Area is not stub.) It says the default value is NO, so what does this mean? For example, if the area is not a stub one, how should I configure the stub cost value? Is it "stub cost no", or "stub cost 0", or just ignore this configuration? Thanks!