I've never been a huge fan of Full Screen Mode, mostly because I am frequently switching between at least two apps. But adding a second app to Full Screen Mode gives the feature an extra dimension that makes it much more intriguing to me.
It's not just that the new feature allows Full Screen Mode to now encompass all of the tasks I perform by switching between two apps, though I do spend an awful lot of time looking at webpages while writing stories. It's also that, at least on my 27-inch retina iMac, it's an awful waste of space.
To bring Split View to El Capitan, Apple has modified Full Screen Mode so that it can display two apps at once. Technically it makes sense. OS X already has one weird mode where apps disappear from the normal desktop metaphor, so why not just extend the capabilities of that mode
The problem is that some of the underlying assumptions of Full Screen Mode can't be made in Split View, and that leads to some really weird interface issues in the El Capitan public beta. (This is as good a time as any to remind you that this is just a beta, and there's plenty of time for Apple to address weird interface issues before the OS X 10.11 ships this fall.)
Most of the issues seem to be around the concept of which app is active. On the normal Mac desktop, you can tell which app is active by shading cues (the active window usually has a shaded title bar and the "stoplight" buttons in the left corner are only colors in the active window) and by the name of the app in the left corner of the menu bar, right next to the Apple logo.
So how does an app indicate that it's active in Full Screen Mode It's a trick question, because there's only ever one app in Full Screen Mode. In Full Screen Mode, the menu bar is hidden unless you move your cursor up to the top of the screen, but it's not necessary as a cue because there's only ever one app running. Apps tend to hide most or all of their window chrome in Full Screen Mode, but again, losing those cues doesn't matter because there's only one app to use.
Except in El Capitan, when suddenly Full Screen Mode is now capable of running two apps at once.
When I was writing my first look at the El Capitan public beta, I used Split View to read Apple's PDF reviewers guide in Preview while taking notes in Notes. Neither app displayed a traditional window title bar or toolbar unless I moved my cursor to the top of the screen. As a result, the only way I could tell that Notes was the active application was when I would see an insertion cursor blinking in my note.
Apps behave differently when they're active and not, a distinction that becomes more important in Split View. When I was taking notes in Notes, I was also scrolling through the PDF in Preview. Mac apps are happy to let you scroll through their content when they're not active--just move your cursor over the content you'd like to scroll, put two fingers on your trackpad, and there it goes.
However, other behaviors aren't allowed when an app isn't active. If I wanted to zoom in on something in that PDF I was scrolling through, I couldn't do it unless I clicked somewhere first. That click would make Preview active--though nothing on my screen would indicate that other than the fact that the insertion cursor in my Notes document would disappear--and then I could zoom and scroll.
The version of Split View coming in iOS 9 doesn't suffer this problem, mostly because there's no abstract pointing device on iOS. When you're touching a window to zoom in, you're touching it--it becomes active immediately. But when I move my Mac cursor over a window in an app that's not active, I can scroll (but not zoom) without ever "touching" it by clicking. Slightly different metaphor, and a very different experience.
I'm not sure what the solution is here--or if there is one. Since you can scroll content even when an app isn't front most, maybe Apple needs to extend that functionality to cover other gestures. Maybe apps that support Full Screen Mode--including Apple's--need to be modified to deal with the fact that they may now be sharing space with other apps.
I still believe that Split View is going to be a productivity benefit to many Mac users. But it's interesting to see how adding one new wrinkle to a longstanding OS feature can lead to some unintended and weird consequences. Here's hoping most of these wrinkles are ironed out before El Capitan arrives in the fall.