Dealing with multiple windows can be a fiddly experience, but Apple could learn from Microsoft
Window management has always been a bit messy on OS X, with controls primarily designed to hide windows by shoving them in the Dock, or shift them between two sizes by clicking the green zoom button. In Yosemite, the green button has been repurposed for making a window full-screen, and the old behaviour is relegated to an å- click.
There have never been any system controls to make it easier to view a couple of apps or documents in a layout that makes them easy to compare or refer to. This is something Windows got right a while back. Windows Snap enables you to arrange windows sideby-side by dragging them to a screen edge. Plenty of third-party utilities for the Mac offer broadly similar features.
Perhaps it is unlikely that Apple will follow suit, given it seems wedded to the idea of full-screen or nothing these days, but if two-up app display arrives on the iPad, it would be logical for the feature to make its way ‘back to the Mac’. In the meantime, we recommend the excellent Moom ($10, manytricks.com) for OS X window control.