Models and Theories in Human-Computer Interaction/Can Fitts’ Law be used in modern world?

Can Fitts’ Law be used with conjunction of other design theories? (Rajan S Thanigachalam)
In his book (chapter 3), Carroll describes nicely about the Fitt’s law and its usage. I agree with the author that the Fitts’s Law is one of the most robust and highly adopted models of human movement. It helps to predict the movement time based on the index of difficulty (according to Fitts’ Law the Movement time is directly proportional to Index of difficulty). It proved that the closer and larger a target, the faster it is to click on that target. However, the author failed to explain when you should not use Fitts’s Law to measure user experience. I feel that there are some areas we should not use the Fitts’s law with the current form, especially when you design system with high-precision inputs.

For example, Power Off slides bar button on smart phone devices (on touch screen). We often carrying smart phone device in our pockets, which can trigger ‘Power off’ commands by accident. In these situations, it required to use high-precision input method such as sliders bar. It uses a higher Index of difficulty to make sure that a command is not execute accidentally. If I think of Fitts’ Law in this situation, I would have designed with a click button where it has low Index of difficulty rather than the sliders bar mechanism to power off the device.

Even though the FItts’ Law is more powerful tool on helping designers to make educated decision in Human Computer Interface, it should be used in conjunction with other factors. I think we need to consider Fitts’ law carefully when you consider about security and the commands that executes infrequently such as unlocking the screen, two-step verification methods for password, turning off the device, wake up alarms and administrative tasks.

In his book, author Carooll would have explained when to use the Fitts’ Law with its original form and how to use it with conjunction of other design theories in this modern world.