Detecting input on edges / corners of the screen. This is very easy to do. You can detect half of the screen for some input and the other half for another. You can detect only the far edges of your screens. Are you using custom rendering? You will want to look at action.screen_x and action.screen_y.
This post by @britzl explains one method for doing this.
Reasons for using this input style: picture book, player movement for a platformer, driving game with steering…