If we're talking about CP, in all the cases I've read about the warrant is basically an excuse to come in and take your stuff and search through it. I haven't heard of any cases where that happened, they found nothing, and then the guy got arrested anyway. Of course so much as a single deleted thumbnail file is enough to put you away for a long time. Being held in contempt of court if you won't, or can't, provide the password to an encrypted volume is a second issue.