In Simple mode, the selected prop animation is mapping to the movements of your mouse cursor in Screen-Based technique;
which is locked to the screen resolution.
This mode controls the object to move on the horizontal or vertical plane, which is very useful if you want a lot of props to pass by in the back scene, such as street cars.
This mode is suitable if you need to rotate a prop round and round, such as a merry-go-round or a propeller.
This mode is very useful if you need to have props act like they are breathing.