In its second form it will show as a blue line at the bottom of the screen whenever you open an article in card view or magazine view. This way you will always know how many articles you have left to read in the current section without needing to close the one that you are currently reading.
Here’s a little screencast to help you see it in action:
If for some reason you dislike it, you can easily turn it off by closing the footer or going to Preferences -> Interface -> Article listing and unchecking Article progressbar.
As always your comments and suggestions are welcome.
The Inoreader team