[tartoran]

To add to this, some shortcuts favorite to some users are used millions of times. Think of all that mental overhead that is saved in the long run.

I am a heavy user of shortcuts and a lot of the times I don't even know what the shortcut is, it's all muscle memory. Intent turns into an action and feedback is both tactile and visual and there is usually an easy way to get back of that also with shortcuts. Using the mouse in some scenarios is like looking through a keyhole. That is not to say that using the mouse is bad all the time, because the mouse beats shortcuts in other scenarios.

To me scrolling using the mouse scroll wheel or using keyboard keys are somewhat similar. Where the mouse workflow is eating the mental overhead is aiming a fly on a small landing 200th the size of the screen thousands of times or more daily.