Every player should know how to hit a one-handed slice backhand. For a one-hander, it's almost an absolute necessity for handling high balls. For a two-hander like Nadal, it provides more reach and better balance when running wide for a ball, as seen here. It also handles low balls better than a two-handed backhand and adds much more variety to the range of ball behaviors you can use against your opponent. A slice carries farther in the air and skids lower on the bounce than a topspin.