It is useful because if you are high functioni g, even through masking, then you do t have the disorder. By defi ition something is only a disorder when you are no longer high functioning.
It doesnt mean the personality trait isnt there, it just means it isnt manifesting in an unhealthy way in order to prevent you from functioning well.
A person who has episodes of OCD obviously has the tendency towards related personality traits. Just that in his healthier state they are not net negitives they are just perfectly normal and healthy parts of a personlity that he happens to have in common with others.