There generally has to be a mouse-mat, or a clean, suitable surface. There is usually a cord which gets in the way of things and can affect mouse movement. There needs to be room on a stable flat surface to move the mouse and hand. Fluff and dust invariably gets into the ball and roller mechanism - meaning that mice will behave erratically unless they are cleaned properly. It seems that it is very easy to learn what a mouse does - children do it in a minute or two.
Pointer devices other than optical thumb trackballs or mice Many laptops have a flat touch panel.
This gives no physical feedback to the finger about the movement of the pointer - but it is nice and compact and not affected by dust. These are often configured by default to respond with a double-click command to the operating system if the user taps their finger on it twice in quick succession. In my brief experience with these, that facility is more trouble than it is worth, and it is best to configure the pad for movement only, and use the nearby switches for the switch functions. Many laptops have a small trackball beneath the keyboard. The placement of this is typically such that the ball must be moved by a finger and the switches manipulated by the thumb or by some other fingers.