This Printpage is desgined for "Show all for all posts in topics with less than 25 pages"
For topics that are more than 25 pages, use that one https://bitcointalksearch.org/topic/show-all-on-long-topics-5112444
I noted it in Hidden pages / features on the forum
are you seeing that "All" button by clicking that you can also see all posts in a nice series or order.(but it has limit)
and regarding print option,
i use that option for : while reading the posts if a interesting thread comes front of my eyes, then i print that thread and save to read offline, when i will have very much free time, or you know that we see our favourite show or movie while eating, just like that if the thread was very good and i print it and read every word of that.