There is always a time when you visit a thread and read something in it and then later on you don't know anymore where you read it. This helps you to keep track of your last visited places, which is very helpful to come back to stuff you want to read again. Thank you.
This is one of the most useful addon I've ever had on my forum. My users are now able to come back quickly to a thread they've seen a minute ago or some time ago without using the back button. This one should be in the XF core.