When you go to the gym by yourself it is a lot easier to skip a day. Having regular sessions will enhance your workout. Being held accountable to show up for a session with another person will make it a lot easier to get to the gym.
When you are paired with a Personal Trainer you know that every workout will be efficient. They can give you the most out of a workout. If you ever have to cut one short, then they can change the workout so that you will still be pushed and have the safe effectiveness of normal session.
A Personal Trainer is certified to do their job. You will be with a person who can provide you not only an efficient workout, but a safe one. They know how to use correct form, and the correct way to use machines.
You workout in a way that is best for YOU! Your Personal Trainer will get to know you, and figure out what methods will work best for you. They can help you read your personal goals and plan a workout for you to reach them.
Throughout your entire session, you have someone there to motivate you. They are there to push you to your best ability. It is always great to have some positive reinforcement during any workout. They want you to succeed in your workouts, so they will be there to push you and make sure that you do.