iOS 9 packs in a whole bunch of nice-to-haves and small refinements that haven't even made it into the official release notes.
Among other things, the operating system introduces a more streamlined Notification Center view in landscape mode which Apple designed to take advantage of the larger screen real estate on iPads.
The enhanced look is based on a two-column layout to allow the simultaneous display of your Today view in one column and your Notification Center widgets and app notifications in the other, so you don't have to switch manually between them.