Essential, I had a customer say he'd like the adventure seeds to be printed in the print books.
I think I was the customer.
Yes, I think it would be great to have everything in a printed form and the seeds are a great help during preparing the campaign. However I also like the separate pdfs, because with them you can prepare them even before the next adventure is released. So, I would second MDC to leave them separated as PDF, but included in the printed books.