Sometimes you need to make several offsets of one linear entity and the distances are variable. With 'Offset Variable' you only have to select the linear entity once. You pick a point on the side you want to offset to and then it's just a matter of entering the values. In cumulative mode the values are added up so the offsets go further and further. In individual mode the value is considered independently of other values you entered. If you are not happy with an offset you can undo the last offset without exiting the command. This way you can make various offsets without having to select entities and pick points all the time.