I disagree. It is unwise to limit a campaign.
Look at Kansas lesson, Newt declared not to go there, Santorum collected 33 and left 7 delegates for Romney.
If either Santorum or Newt reach >50% in the state level or congressional district levels, he will collect ALL the allocated delegates leaving none for Romney.
If they both campaign for the same delegates at the same CD or state, they will never achieve >50% votes, therefore, the allocated delegates at that particular CD or state will be awarded proportionally to all three candidates plus Ron Paul.
Unfortunate! Nobody listens.