Although relativization disambiguates, it does not eliminate borderline cases. There are shorter pygmies who are borderline tall for a pygmy and taller Masai who are borderline tall for a Masai. Words are only vague indirectly, by virtue of having a sense that is vague. This contrast between vagueness and ambiguity is obscured by the fact that most words are both vague and ambiguous. The contrast is further complicated by the fact that most words are also general.
Generality is obviously useful.
By gauging generality, we can make sensible trade-offs between truth and detail. This precipitates many equivocal explanations of vagueness. For instance, many commentators say that vagueness exists because broad categories ease the task of classification. If I can describe your sweater as red, then I do not need to figure out whether it is scarlet. This freedom to use wide intervals obviously helps us to learn, teach, communicate, and remember.