If you're interested in putting the right people in jail, you aren't doing any favors by being sloppy. This isn't said enough. Destroying evidence isn't a "favor" to the all the innocents criminals prey upon, any more than blowing the rent money to take your kid school shopping is an act of love.
This article available online at:
http://www.theatlantic.com/business/archive/2009/12/not-helping/32524/
