That is a fantastic question although I’m not sure I’m totally qualified as I haven’t used a pickleball ball machine yet. That being said, I’d imagine 3rd shot drops would be perfect to practice with the machine. You can work on your footwork and making sure you’re getting your contact point the same for every drop. I would also have the machine locate deep “serves” to work on your return. Focus on moving through the return and getting a quick first step towards the kitchen line. Also make sure that your return is landing deep in the court ensuring a tough 3rd shot for your “opponents”.