In my opinion it depends on the client’s goals and fitness/health level. I wouldn’t have an obese client wanting to decrease body fat performing isolated movements…and then I wouldn’t have a bodybuilder trying to gain muscle mass performing stabilization exercises on the ball. (unless an assessment proved the need otherwise due to some degree on poor staility)
Like many have said it depends on your goals. Many say we train movement patterns. Bodies know movement patterns and not a single muscle looking to get bigger. If our goal is hypertrophy and bodysculpting then isolating muscles can be very beneficial. It is also beneficial when we’ve done some manual muscle testing and we know a certain area is weak.