It's a simple and effective training method to add "filler" exercises to net sessions to help with fitness training. You know the type of thing; adding in press ups and sprints between balls to increase fatigue and bump up fitness. Here is a perfect example. We have done this kind of work for years.
I'm sure if I asked you to name a few simple things players could do, you quickly think of exercises like press ups, chin ups, squats and lunges. How about we add a few more into the mix that will also prevent injury. Plus, it gets a bit dull doing lunges, so why not mix it up?
Naturally, you won't want to run fillers at every nets you do. It depends on your goal for the session, but the fact is that these movements tick a lot of boxes: They save time, they reduce injury and they test your technique under fatigue. If you want to do those things, get going!