There are certain features only registered attendees (= with an account) can use:
Booking a seat and interacting within workshops (ask questions, vote in polls, download files, etc.)
Rating sessions
Networking
Other features, like asking a question and voting in a poll within lectures, receiving Newsfeed notifications, viewing Custom menu items, creating personal agendas, and more, don't require a profile, and therefore, even anonymous attendees can use them.
