This is possible for some reasons, cause it takes time for someone to read through a post, and then start typing his response for it to be constructive and reasonable for fellow users to read.
I do this in other forums where I open multiple threads and type in my response, copy it down in a saved document for the right time I wish to make the post. I use this methods mostly when I have a very occupied day's activity outside the internet, so as to meet up my daily task in the forum.
Though, one thing I do, is at the point of posting, I still read through, so as to do some corrections, either remove or reconstruct some sentences, which takes a little more time for the entire post to be made.