Though The Odyssey is primarily a story about men, it features a number of important women. For the most part, a woman's function within the world of The Odyssey is to influence the deeds of men either negatively or positively. Athena and Circe illustrate this trend perfectly, as one exists primarily to help Odysseus, while the other exists to antagonize him.
Athena: Athena is the goddess of wisdom and is essentially Odysseus' biggest fan. She protects him from Poseidon's wrath, urges Telemachus to search for his father, and encourages the king of Ithaca when he contends with the suitors for possession of the palace. As such, she exists primarily to help Odysseus accomplish his most important tasks, and the king's journey would be far more perilous if she did not exist.
Circe: Circe is the enchantress who lives on Aeaea an turns Odysseus' men into swine. She is the main antagonist of the Aeaea episode and primarily tries to hinder Odysseus' attempt to get home. As such, she represents the opposite of Athena, acting as the woman whose main function is to stop the men in the poem from getting what they want. If she weren't in the poem, Odysseus' journey would be considerably easier (and, by extension, considerably more boring). The case can be made that she's not all bad, as she does amend her ways and entertain the wandering sailors for a year after Odysseus gets the better of her, but she's most memorable for her stint as a villain.