I think the error tag isn't used for every error there is, but rather if the said error is prominent or otherwise irritating enough (For instance, I've been tagging it if the eyebrow merges with the bangs' outer line which can ruin the whole image for me at least).
That said, at least with its current wiki, the whole tag is problematic, as it's supposed to be exclusive from bad_anatomy (and therefore from other bad_* tags). If we change the wiki (which I do recommend) I can see such BUR be worth it.
As for usage, I don't know how many blacklists these, including error, but I see it being totally worth it to do so if such tag(s) exist. As from my side, as an approver, I quickly check tags before or while I am first glancing the image, and if I spot bad_* tags or error tag, I seek for that first, and evaluate the whole image after. It hastens my approving process tremendously in some cases.