Exercise machines revolutionized the fitness industry back in the 1970's. They created the current gym. To me, the great benefit is that they created interest causing people to go to the gym and get fit.
Anything that gets people moving has merit.
However, these machines also allowed big gyms to hire minimum wage people who would walk you through on your first visit and point out the features, saying this machine is for abs, this is for legs. Now go to it! Kind of like a school where they walk you to a desk and say here is a math book and a science book and a literature book, come here three times a week, teach yourself and get smart.
The problem with machines is that they alter the way your body naturally moves and constrain your range of motion. By limiting your range of motion, you activate fewer muscle fibers and burn less fat and get poorer muscle definition. A bigger problem is that they can cause excessive strain on your joints.
Perform exercises that allow you to use your full range of motion and mimic what you do in everyday life like lifting a bag of groceries.