I dunno, I just don't find them particularly useful. The time it takes to click the arrow is not that much less than the time it would take to hold down the arrow key on your computer or laptop to get to the top of the page. It's more of an alternative method than a time-saver.
plus in a forum with little activity, I don't see why anyone would be in that much of a rush to get to the top or bottom of the page.
that's just how I see it though
