It has been really interesting for me to see how much the trend of print mockups has been on the internet as a way to showcase your work. Not so long ago when I first was adding portfolio items to behance I was using just screenshots of my files and now I take the time (which is getting quicker and quicker) to make mockup images. They really do tell the story better and are instantly recognisable. It is not until I see the two side-by-side that I realise this is a trend that will not be going away and this is something I am very happy with.
It certainly makes a difference when showing spreads of a book. Previously I felt the need to show the spine and edges otherwise there is no context.
I really do not think the difference is as profound with the cover but certainly, it is more obvious that this is a book cover and not a flyer or something else.But when showing something really quite big, like a billboard, the mockups are simply wonderful because it is so much easier to understand the scale in this context.