There have always been a couple of minor issues that have bothered me about how the Sidebar and Inspector work in OmniFocus 2, but the new Split Screen mode in El Capitan seems to have brought these to the forefront.
Firstly is the fact that there seems to be an odd lower limit for how narrow a window can be. Even with the Sidebar and Inspector turned off, so I’m looking at nothing more than a task list, the window can’t be reduced below what appears to be an arbitrarily fixed size, leaving a lot of whitespace and now taking up valuable space from other apps that are sharing the split screen.
Further, the Inspector slides out to the right and increases the underlying window size in the process (e.g. even after the Inspector is hidden, the window remains just as wide as the combined task pane and Inspector view). This has always bothered me, as I prefer to keep secondary windows around that just show task lists, and these windows “grow” as soon as I need to pop out the Inspector to check more details on a task or make a quick modification, requiring me to resize them again afterward.
In Split Screen view, however, this actually causes OmniFocus to move to its own full screen view, as the window suddenly takes up more than half of the screen, which of course requires a lot more fiddling than makes sense in order to get the window back to where it belongs.
Prior to Split Screen view, I would have, been satisfied if hiding the Inspector returned the window back to its original size (ditto for the Sidebar). Now, however, it seems that it’s almost necessarily for the Inspector to be available as a panel, much like how the View Options are presented (which, BTW, work beautifully in Split View).