Sometimes a voice (picture or video) is worth a thousand words - adds teacher presence  and immediacy.

An important proviso; like any technology, it can be done pointlessly, badly, counter-productively. 

As much as anything, inclusion of podcasts usually implies that the creator cares enough to put effort and personal energy into creating a good learning experience. The caring of the teacher is among the very top factors in motivating learning in an educational/training setting. It is very hard indeed to extricate the enormous benefits of that simple fact alone from anything that is innately valuable about podcasts themselves.

A further benefit is that it almost always increases time on task: time spent listening to a podcast provides more opportunity to think about, reflect on and generally connect knowledge gained in other ways. Again, this is not so much a necessary feature of the technology itself as a useful side-effect of using it.

Animated gifs come to mind. Just because we can do it doesn't mean we should. That said, I know that well-designed podcasts can improve engagement and help students grasp elusive concepts. (I learn a lot from YouTube )

However, I think it is more foolhardy than brave to venture beyond a talking head without some support from a visual designer and/or videographer. The medium is the message, and badly designed (or undesigned) media can convey the message "this is silly," or  "this person is an amateur" even though you may be an expert in an academic field.

Where podcasts have evolved I still think of them as audio content even though video podcasts seems to be growing.  Never thought of it as talkiing ebooks. Streaming content fits with the definition of what a podcast is which used to include access it via an RSS feed.  

To me, it's audio, but the 'cast' part implies a continuously (regularily or irrgularily) updated clip, about something that just happened around a topic (the reason for people to subscribe), plus an archive of old clips. 

Pod casting? Is that like throwing away the shells of the peas?