I think using the "thanks" button transcends thanks.
One can "thank" even if one does not "agree" with a post.
I sometimes use this feature to show I have read the thread, and/or post for some reason. Some people are very sensitive to being ignored, and the button, shows them at least someone is there in some capacity. When conversation is holding its own, I will only thank, but not join in, sometimes.
I don't thank each and every post however, because I read so many of the forums, I'd end up EVERYWHERE!
The "thank" button had a somewhat rough beginning, with some people years ago a bit unsure about it, but as time has passed, it has been accepted and used often now. When visiting other forums on the net, I miss it's presence there now!
It is a new feature that vBulletin put in on some upgrades we had a few years ago. Like some of the other features here, it is
voluntary. Doc was very generous and understanding about it.