Let me also start off my saying that the newly enviable "thigh gap" that women are after, is mostly based on genetics and the shape of your pelvis, not your body fat or muscles. Not to mention, an athletic woman will have her inner thighs touching. Squats and leg work will make sure of that, but they will also make sure you have a killer ass unlike those girls with their inner thighs not touching, but the flat booty of a 13 year old boy.
So...why should you skip this popular gym machine? "Think about it, our leg muscles are designed to move our body during walking—sitting in a chair and moving the legs in and out does not work the muscles the way they are designed to move our skeletal structure and is a complete waste of precious training time," says Pete McCall, an exercise physiologist for the American Council On Exercise.
Instead, train the muscles of the inner thigh, hamstrings, and glutes with single-leg Romanian Dead Lifts, (or RDL's) McCall suggests.
To do single-leg Romanian deadlifts (pictured below and in video), stand with feet together and knees slightly bent, holding a dumbbell with left hand. Engage abs, and balancing on right leg, hinge forward at hips, lifting left leg behind hip until chest is almost parallel to the floor. Keep spine naturally straight, abs engaged, and return to start. Of course, this is not the only thing you can do to tighten those legs and inner thighs, but it sure is a much better start than sitting in a chair and squeezing.