For rehab a machine provides focus on specific muscles but it has long been known that free weights are far more effective. Body builders use free weights and not machines to gain and then to maintain their physique. The older a person is the more they can benefit from the use of free weights that improves balance and reduces the chance of a fall.
Machines are great for gyms as the owner does not need to employ a trainer/spotter and so makes more money from his customers.