Mixing Up your raises

In Dan Harrington's Harrington on Holdem I he writes that a good multitable player mixes up his raises. He advocates raising 3x the Big Blind 35% of the time, 4x the Big Blind 35% of the time, and 15% for 2x and 5x the BB in order to keep your opponents guessing.

Is there a certain situation where 2x the BB is the right play? We always discuss the 2x the BB raise as a donktastic play.

Should this be used on occasion and where?

The only thing I could think of is when you have Aces on the button and a weak player in the SB and a loose one in the BB.