A compact keyboard does not feature a numerical keypad. This allows users to position their mouse closer to their keyboard. Research shows that 90% of all keyboard users rarely or never use their numerical keypad.
A compact keyboard is more comfortable to use, because it reduces the distance to your mouse (Cook C, et al., 1998). This limits the strain on the user's lower arms and shoulder.
Dark letters on a clear background are easier to read (ISO 9241) and contribute to an increased productivity (Snyder, 1990).