This invention would bring artist's the ability to add expressiveness in a easy and intuitive way.
Music: You can add a vibrato and brighten a note simply applying more pressure to the surface.
Art: Applying more pressure widens your stroke or darkens the color.
Games: You can gage the player's determination by how hard the button is pressed, or how soft/hard you can strike a golfball.
Word Processing: heavy typing bolds or caps your text.
Science: Change a variable...