How much do you prepare for seminars?

Edut: these are undergrad seminars

Caveat that I tend to over-prepare. But I always have a mini-lecture--three slides laying out what the topic is--and then I prepare sets of questions on the general topic and on the specific readings that I provide them ahead of time.

But then I think back to my college seminars (early 2000s), and we'd just be assigned a few chapters of something or some articles, show up, and the Prof would say "so what do you think?" And we'd talk. Or some of us would.