You could have the greatest motion with your hitting arm and still have trouble hitting your serve consistently in the service box. The reason? If the TOSS is not consistently in the same spot your racquet face can be tilted down too much or tilted back too much at contact. Just a one degree difference of the racquet face, tilted back or down, can make a six foot difference in where your serve lands.
The Toss Is The Most Important Part Of A Consistent Serve