Snooping has an adverse affect if you are snooping on a kid like Jumper, who has nothing to hide. The funny thing is, Jumper doesn't care if I go in her room, am a FB friend, etc. I don't snoop on her, but I could and she'd just roll her eyes. Julie was doing serious, dangerous drugs and the cops were dropping over and we had to make tough decisions as to how to handle her, as well as help her. In no way did it affect our eventually close relationship. In fact, she knows and has said she understands that we were just trying to keep her safe, now that she is no longer on drugs. Most of our drug using kids are unsafe and sometimes we don't know HOW unsafe because they don't exactly say, "Hey, mom, I tried crack today and I am going to do it again." They already don't trust us because drug users don't trust anybody because they are always on edge of being caught.
I personally (and this is JMO) don't think that you should snoop if you only want information that you aren't going to act upon. All that does is cause yourself anguish and pain and it doesn't help your kid and it is basically for nothing in my opinion. But if you are trying to save your child's life, there is often no alternative. A policeman told us that if there was drugs in our house, even if they were not ours, WE could get arrested as there was no way to prove they were not our drugs. What if you have little kids that you still have to raise? You can't allow your drug using child to get into legal trouble and involve you...especially if you have young 'uns to raise.
Once Julie left she was free to do as she pleased and she, as everyone knows, stopped using drugs. But it did take a while. However, since she was not in our house, she was no longer in any way our responsibility, including where she kept her drugs since we could not be held accountable.
So there are many things to consider with kids who use drugs. Some parents are die hards about not going through their kid's things, but I'm glad I did. And it wasn't held against us.