I think your overthinking it, at least on this particular forum. Like others have said, it is a good way to acknowledge a comment, without leaving a comment. It keeps the threads from becoming cluttered.
When I first joined this site it was the old format. I got off pipes for a short while and was back to cancer sticks, then back to pipes, life got in the way yada yada. I got back on the forum and noticed the different format, but didn't really think twice about it. Like others, I have notifications turned off. It doesn't appear to have changed the way members interact on here as far as I can tell. It just makes the threads a little less cluttered.
When I first joined this site it was the old format. I got off pipes for a short while and was back to cancer sticks, then back to pipes, life got in the way yada yada. I got back on the forum and noticed the different format, but didn't really think twice about it. Like others, I have notifications turned off. It doesn't appear to have changed the way members interact on here as far as I can tell. It just makes the threads a little less cluttered.