Ah - multiball technique is a good question. Do you try to trap balls during a multiball or not!
For me it depends on the game and what is required by it, but generally I will still try to trap a ball or two and actually shoot for something. For example, on the Cactus Jack's I will often try to shoot the left ramp continuously during multiball; but keeping both balls in play during a Cactus Jack's multiball is more important than trying to trap one or both of the balls as hitting the 'throw' shots during multiball really gets your score going.