If you use multiple monitors on a regular basis, you might care about how Mac OS X Lion handles Full-Screen Apps when hooked to an external display. In short, it doesn’t work that well.

To be clear, multiple monitors work fine in Lion, everything is the same as past versions of Mac OS X, you can mirror or extend your display as usual, that’s all dandy. The problem arrises when you put an app into Full-Screen mode; this causes only the default display to go into full-screen view, and the external screen becomes just a large and unusable linen wallpaper filled placeholder.



Full-Screen Apps Built with MacBooks in Mind?

Looking at Apple’s web page for the Full Screen App feature, you’ll notice there are no desktop Macs shown, it’s all about the MacBook Air, so it’s entirely possible this feature was developed mostly with laptop users in mind because it benefits them the most.

Considering the use-case scenarios, you probably have plenty of screen real estate available if you use an iMac 27″ or if your MacBook Air is hooked up to a large 24″ external LCD. The pixel-saving feature of Full Screen apps is just less useful on a large display than on a smaller screen. Maybe Full-Screen apps were intended for smaller screens to begin with? The feature shines on the MacBook Air 11.6″ and other portable Macs, how useful is full-screen Safari at 2560 x 1440 anyway? As a commenter on MacRumors Forums says, “full screen apps address an issue specific to small screen devices and for larger screens that issue doesn’t need addressing”.

It’s Called “Developer Preview” for a Reason

Finally, remember that Lion is still a “Developer Preview”, meaning things we see now may not be finished and may ship differently in the final release next month. The way that Lion is currently handling full screen apps and external displays (as of DP4 build 11a494a) could be indicative of an unfinished feature. Maybe it’s even a bug? Maybe it will change come time to ship?

Or maybe not? If this is how Lion works with full-screen apps, it’s not that big of a deal, you can always just avoid the feature when your Mac is hooked up to an external display.