Federated access management can make things nice and simple for both the user and the service they are accessing. By logging in to their home organisation the user can have that organisation release relevant information to the service - "I am a student", "this is my e-mail address" and so on. And because that information comes from the organisation, the service is likely to consider it more reliable than information self-asserted by the individual user (especially if being a student entitles you to benefits such as site licences, reduced prices, etc.).