What is difference between actions and robot class in selenium code example

Example: disadvantages of robot class in selenium

Keyword/mouse event will only works on
current instance of Window. suppose a
code is performing any robot class event,
and during the code execution user has moved
to some other screen then keyword/mouse
event will occur on that screen.
Most of the methods like mouseMove is
screen resolution dependent so there
might be a chance that code working 
on one machine might not work on other