The beauty of using a stability ball for chest exercises is that you get extra core work at the same time you work your chest muscles. (all-about-arm-exercises.com)
Sitting on the ball just adds a little extra core stability challenge, but you can put your mind to it and stabilize your core at your desk too. (verywellfit.com)
If you're short on time and want extra core work you need to step away from exercise machines. (thrivepersonalfitness.com)