Odysseus doesn't need to visit the underworld for the purposes of the plot
there is no direct consequence to his visit
he leaves Circe in bk 10 and returns to her in bk 12
she gives him the same advice about his journey as Tiresias gave him
Agamemnon gives Odysseus advice to make a secret approach when he returns to Ithaca, but surely he is too clever to need that advice
it results in problems of continuity - somebody would've noticed Elpenor's body; Telemachus must be 13, but he is described as 'in peaceful possession of his lands', as though he is much older
fits in well with epic, as it is another adventure on a long journey
tells us more about Odysseus' character
emphasises his heroic qualities: only heroes like Heracles can go down to Hades and return
Trojan War heroes are relevant to his past and his heroic status
Achilles, Agamemnon, and Ajax are all seen as his close companions
explains the presence of the suitors - Laertes has left in despair and so is not in the palace to take control
theme linkage of:
family - catalogue of women, Tyro, Antoine, Epicaste (Jocasta), Leda, Phaedra all have family problems - compared to Odysseus and Penelope
loyalty - Agamemnon and Clytemnestra are compared to Odysseus, highlighting Penelope's loyalty
justice - the Suitors will be punished, like Sisyphus and Tantalus
storytelling - when Odysseus pauses, the audience ask him to continue. This underlines Odysseus' skill in storytelling
value of life - Achilles tells Odysseus that life is precious - he would have anything rather than death