What’s with the combos?

I’m an avid reader, mostly of ebooks, so I’m wondering, what’s with the combos? Ebooks are combined with audiobooks, and print book/ebook or audiobook pairings are common now. Can some reader of this blog tell me why a reader would ever want to buy such combos?

I can imagine audiobooks being useful for a commuter or jogger who can “multitask.” Whether such people are actually “reading” anything complex that way is questionable. Maybe they need the ebook or print version to go back and understand...