My theme here, right now, is called The Box, and it meets all my requirements for a good WordPress theme. It hasn’t reached the WordPress.COM repository yet, but it should, methinks.
There are trends in theme creating, just as in fashion and everything else, it seems.
My theme doesn’t have it, so I can’t show an example.
I’m in full understanding why they use it; it’s nice to get the sidebar out of the way … makes for a cleaner reading experience. Also, and perhaps more importantly, most people read on mobile devices nowadays, and it saves space.
However; I’m not a big fan of the hamburger menus. As much as I love many of the themes, I see this as a downside. Even if people actually know what this icon stands for, I highly doubt they click/tap on it. «Out of sight: Out of mind!» is an expression that popped up in my brain.