Sure, it's possible to prepare ahead and also afterwards. But this is so time-consuming, I mean after all everybody has to decide that for themselves but IMHO Pareto-optimizing that means not visiting most lectures. At least that's how I studied and it worked out really well. But I agree with you one can seek a lot of value from it, but that doesn't limit itself to 1.5 hours sitting there and listening. But rather being really concentrated for 1.5 hours, and spending time before and after.