Lectures are good for the lecturers because they can

(I=Indra   P=Professor)
I: Good afternoon. Professor Green. Thank you for your time today. I wonder if you could explain why you think it is important for us to attend lectures in a course that we are studying?
P: Well, despite the increasing dependence on online communication these days, I do think it is important. Apart from delivering the content of the lecture itself, I believe that there are some general communication benefits from having large groups of students together in one place. For lecturers, it is an opportunity for us to address many students together at one time. For students, it helps you to feel part of the wider learning community who are following the course. You can interact with each other both before and after the lecture to discuss the ideas and content — networking with each other and comparing your notes.
I:  But isn’t most of this achieved, as you said, these days through online communication?
P: Well, lecturers do communicate with students online, of course, but we usually only give a summary or notes of the lecture, so there are significant differences. When you go to lectures you get more of an insight into what the lecturer considers important. We give additional commentary and anecdotes, and by voice emphasis we can alert you to the key concepts, theories and issues of the subject. By not attending lectures you might miss crucial information about what we are expecting in an assignment. You know, these extra things can make a difference.
I: OK. But there are tutorials. There is a lot of interaction between students and lecturers in tutorials. Can’t all this be done in tutorial discussion groups instead of having lectures?
P: Yes, to some extent. But during lectures, the lecturers can sensitise you to the debates and the controversies that are dealt with in the literature. This can help you think more critically about the subject. So then, when you come to the tutorial, you will be able to come with some questions and ideas for discussion. The result of this is that the tutorial class will be more beneficial for everyone who attends.