What are the consequences, in literature and in art, of Roland Barthes's affirmation of "the death of the author"?

Roland Barthes changed the face of criticism with his theory that works should be considered alone, in a vacuum, for their own merits, rather than as extensions of their authors. For example, prior to Barthes, the poetry of Oscar Wilde would usually have been viewed in the context of the biography of Wilde as we know it: that is, we could often assume the voice of the poems to be that of Wilde, known to be homosexual and to have suffered through a criminal trial.
However, Barthes's theory requires works to be viewed alone, without superimposing the biography of the author onto the work itself. Thus, post-Barthes literature is permitted to be interpreted in multiple ways, with every possibility allowed by the text entitled to equal consideration, whether or not the author would have approved of or endorsed it. A modern example could be the casting of Hermione as a black actress, because although the text by JK Rowling (who is white) in her Harry Potter series does not explicitly say she is black, it also does not say she is white.