I would like to add to Traveler's comments:
There are some posts to which we don't have an answer to or that its topic may not apply to us. We can in these cases do a "bump".
What is a bump? Glad you asked!
A bump is when you reply to a post that has "0" replies and that has fallen way down on the list with BUMP in the reply. This will bring it back to the top of the topics list, thus making it more prominent once again so that others can see it and reply.
Also, there are posts where someone is posting a link or commenting on an article that they have read online. It is good forum practice to reply with a "thank you" to let them know that you enjoyed their post or that you found it interesting.
I myself have posted before about
a particular article that I found on the internet which I thought was earth shattering and the greatest thing since sliced bread, yet, when no one replied about
it, well, it really bummed me out... so yes, it is nice when we say "thank you"