It is my habit to open the forum to the main index. I then open tabs to the sub forums I'm interested in reading. After that, I go to the last tab opened and then open a thread in another tab.
Many of the threads have posts which contain links to other sites. OK. I go to that site (in a new window), read the information and usually, I get one or more links to yet more sites that contain info I want to read.
By the time I close all those other windows, I go on to read the next thread.
I've just spent more than my 20 minutes of alloted time and the next thread takes me to the "last read post." ... Only several people have made posts while I was "entertained" elsewhere. So I get taken to the last post of the thread.
Now I have to manually browse back up to where I remember reading the actual last post, in order to read what was posted since I was actually online last and while I was away (at other sites).
If we had persistent read-state tracking. I (and by extension, you) wouldn't have to fiddle with all this. I could simply click on the next thread and be where I should be. No fuss, no muss.
It isn't at all hard to click on "Forum Tools" to get to the "Mark This Forum Read" button, when I'm done.
For those of you that use the "New Posts" function, read what you want and then go back to the index and select "Mark Forums Read" when you are done. The next time you are here, only the new posts (since you were last here) will be shown.