What are the software differences between a standard and plus version of an iPhone? (e.g. 7 vs 7+)
iPhone X Plus vs. iPhone X features:


Horizontal rotation on home screen, which can speed up folder browsing.
Uses regular horizontal size class when device is rotated to landscape orientation. This allows apps such as Notes to display the list of notes on the left hand side and the note details on the right-hand side in a split pane view.


iPhone 7 Plus vs. iPhone 7 features:


Bokeh effect as @tetsujin mentioned.