O. M. G.
I did not know that. (And I’ve been here for a while.)
That could maybe come in handy if I want to see whether two or three posters really have started monopolizing a particular thread, as it seems sometimes happens.
If you ever venture into the Game Room and take a peek at the various mafia games, you’ll see we use that feature all the time. So at least in one little corner of the board, it’s phenomenally useful. 
You know, never once in all times I’ve been on this board have I ever clicked on that reply link. That’s so weird.
I was unaware of that feature, too, Fear Itself, and that adds to the gee-whiz nature of it.
I have used the “Who Posted?” feature on threads where I have been a heavy participant, to be aware of my tendency to “monopolize” topics I’m interested in. I have even quit posting when I became aware of that aspect of my interest in the issue. So it’s a deterrent at times.
But, on the other hand, I have used it on some threads with over 50 individual posters to try to decide which Dopers are most likely to be interested in the topics I am. I even had a thread or two on “Who is in your Doper Gang?” or words to that effect. Some of my results were quite surprising to me.