Many golf drills force you to exaggerate the desired method in order to cure you of a bad habit. This one is a good example.
Done correctly, your swing path will be severely inside-to-out, sending the clubhead and ball well right of where your body is aligned. This is the opposite of your usual over-the-top path, the root cause of slicing.
To route the club properly, you’ll have to drop it onto a flatter (more horizontal) plane on the downswing. This will feel foreign at first, and you may fear that your shots are going too far right. Don’t worry. Again, the drill’s purpose is to fix your poor swing path and replace it with a correct one.
Like many drills, this one is great as a pre-round warmup – especially when you’re still working to eliminate that slice. Hit your first 10 shots this way before proceeding to normal swings.