Hi there!
Although the image you added to your question isn't accessible (being available on a local IP), let me elaborate the "Show the next assignment when completed" feature:
Suppose you have three activities say A, B & C in your process definition where activities A & B are connected and assigned to the same user (say U1) and activity C is assigned to some other user (say U2).
Now when the user U1 completes the activity A by submitting the form associated to it, the userview can either redirect immediately to the next form (bound to activity B) or just notify the user that the form has been submitted and put the pending assignment for activity B in his inbox.
This is where the "Show next assignment when completed" comes into picture. When ticked, it allows the next assignment to be shown to the user immediately when the previous activity is completed instead of just showing the "Form Submitted" message and putting the next assignment in his inbox.
Hope it makes sense!
Thanks