Completely radical for his time, Jack Lalanne opened one of the nations first gymnasiums in 1936. He is credited with creating the prototype for both the Smith Machine & Leg Extension. The debate rages on however.
Are machines effective and should you use them?
Simply put, not all machines are created equal. Since Mr. Lalannes first drawings, gym machines have become increasingly sophisticated. Seats and seat backs on newer ones are styled to form fit more naturally. Modern machines no longer force one into unnatural positions and grips are better. However advanced exercise machines become, not all gyms are equipped with the state of the art, so finding what works for you is key.
Ask any gym rat or bodybuilder, Jack’s Leg Extension is still widely used as it effectively targets the quadriceps. (See if who you ask can tell you who he was.) The Hamstring curl is also a must for many due to the fact that muscle group is typically hard to work in general. The Chest Press tends to be staple as is the Preacher Curl Machine.
A solid point with machines is that stabilizer muscles are not fully engaged. In the Overhead Shoulder Press your primary muscles activated are the deltoids. The stabilizers kick in with the triceps. With a Smith Machine less of your stabilizers are used however there are safety latches if you are going heavy.
A good workout should be varied including free weights, body weight exercises and even a machine or two. A sensible approach would be to keep lighter weight/higher rep sets for machines. If your workout partner flaked or you don’t have a spotter a machine can be a good alternative. Too much of anything isn’t good and machines shouldn’t be used as substitutes but rather as supplements, additions to your program.