What's the big deal with de Saussure and structuralism?

Hey folks, Can somebody explain to me what the point of linguistic structuralism is in literary theory? I have seen tons of lectures on the topic but all of them only repeat the same few talking points: The lingusitic sign gets its meaning from difference, and the signifier ist connected arbitrarily to the signified, diachronic and synchronic investigation, langue and parole and so on... Ok, so what? All i hear is about this abstract notion of language but i never have seen an example of usage of these ideas in literary theory, how in the world is one supposed to make use of this concepts when dealing with literature? Same thing with literary semiotics, are there people who actually use these things in practice, if yes, how?