My new Mac mini’s Displays preference panel allows me to spin the display through 90, 180 or 270 degrees. Here’s what it looks like at 90 degree spin on my Mitsubishi Diamond Pro monitor:

Sideways OS X desktop

This feature is not enabled on all Macs. On some (Power Macs, some PowerBooks, Mac minis), it is visible by default. On other machines, a hidden command makes it available. On most older or low-spec machines, it simply isn’t available and won’t work. It all depends on video cards.

Much of the discussion I’ve seen about this feature on the web has been restricted to how cool it is.

There’s no doubt it’s cool, but I want to know why it is there in the first place.

Maybe: Apple wants to cater for users who own swivel-capable monitors that can display vertically. Or, Apple plans to announce a new series of displays that all have a new, swivel-enabled stand out of the box.

But there’s something about this that bothers me. For some time now, Apple has been pushing hardware and software that maximizes use of horizontal space. Quicktime, iPhoto, iMovie, GarageBand, the Dock - all are designed, by default, to stretch out sideways. That’s why they look so great on a 30 inch Cinema display. It’s also why the smart people put their Dock on one side of the screen, because vertical space is at a premium and by moving the Dock to one side, they can reclaim a few precious pixels at the bottom of the screen.

Rotating the screen to a vertical position throws all this stuff out the window. Luxuriant sidelong apps suddenly look cramped and uninviting. But apps related to reading and writing start to work better.

So maybe it’s something else. Maybe Apple is working on an unannounced device in which a rotated screen makes sense - some kind of tablet or laptop with a swivel screen; something that could be held casually in one hand and used in situations where people want to read, and write.

Anyone got any better reasons?