Each type of suspension requires a specific method of ball joint inspection. Some must be checked with suspension unloaded, some must be checked with the suspension loaded. Checking the front upper ball joint on a model S requires the suspension to be loaded. Put a floor jack under the wheel hub and jack up the suspension. Grasp the upper link and attempt to move it up and down to detect ball joint free play. Grasp the knuckle/spindle right under the ball joint and attempt to move it inward and outward to detect ball joint free play. If you leave the suspension drooping (unloaded), the weight of the suspension and the tension of the spring will be pushing the ball against the socket and the ball joint will FEEL tight and good even though it might be worn and loose.
Most cars on the road now use a mcpherson strut front suspension. Unlike the model S, those ball joints must be checked with suspension UNLOADED. Suspension design and geometry dictates whether ball joints get checked with suspension loaded or unloaded.