What do you consider an acceptable use for margin or a pledged asset line?

Ultimately credit is a way to either boost returns and allow for flexibility without just selling or a way to increase risk and open the door for ruin.

What do you consider acceptable uses for credit with your shares as collateral? Is it part of your strategy, a way to get things done with credit quickly that will be paid back as soon as another loan is issued or just an in case of emergency option?