If I have detailed and important information I want to convey you, which makes more sense:
(a) I write it down and give it to you in print.
(b) I tell you to show up at a given place on a given time for me to blurt it out as a long monologue and hope you catch it all.
Option (b) has number of disadvantages built into its very format. The transmission of information is artificially paced at the rate at which I talk, so if your natural rate of absorbing this material is either higher or lower than this then you will be bored or overwhelmed accordingly. The fact that I go on talking continuously also means you cannot reflect on the information I give you until later, forcing you into passivity of thought during the time we are together. The presentation is also uncompromisingly linear: if a point depends on a previous one in a way you did not anticipate, you cannot go back an reconsider the earlier point in this new light, potentially making it impossible for you to understand the latter point. These obstacles to learning are logical consequences of (b), but they are completely needless since they can all be avoided by opting for (a).
Add to this the logistic absurdity of (b) applied to an entire class. Every single student has to structure their life around this one time slot. They set their alarm clock (even though sleeping would have made them much better mentally prepared to take in the information), commute during the worst hours, and rearrange work and family obligations in complicated ways. And for what? So that they can all sit in the same room at the same time to listen to someone basically dictate a textbook to them while they take “notes.” The university, meanwhile, incurs great costs for the large lecture hall and the expensive textbook-parroter, especially since the charade has to be repeated again year after year. Why not save a ton of money and human costs on all this logistic madness by using a video lecture instead, or better yet skip the parroting-step altogether and just have the lecturer write the notes straight away? That would be option (a), which is, by contrast, incredibly efficient, since a text is amazingly portable across time and space: it can be shared with anyone anywhere, as well as preserved for future generations, at virtually no cost.
But there is a way to make sense of this very costly enterprise of herding students together in one room. Namely: use the possibilities afforded by people learning something together; use the human resources and potential that we have paid so dearly to bring together. Discuss, think aloud, question, collaborate. Indeed, this goes very well with option (a), for reading in advance and having the text concretely in front of us is the natural starting point for such discussion and active engagement. Only of we take advantage of this precious opportunity for students to engage with their co-learners is it rational to have a scheduled class in the first place. Otherwise we could all just as well sit at home and read a book and save ourselves a massive amount of trouble and money.