I live with my grandparents and my grandmother does some so called snooping but she also gives me my freedom. Theirs a fine line to being a parent. You have to set reasonable guidlines while not being overly harsh. Face it your kids are gonna try drugs and etc. You can't stop that and if u try harder to stop them the more their gonna wanna try. Now as a teenager you need to try cigs,beer,weed ,sex etc now some teens get going crazy doing "hard" drugs like heroian or cocaine as a parent I would only snoop ever so often just to make sure nothing insane was going on. Now if I found they were smoking weed Id give em a talk and tell em my views and what not to do but I wouldn't ground them Besides giving advice and trying to control your children by the time their 14-16 theirs nothing you can do. If your teenager son/daughter wants to do something bad enough nothings gonna stop them except if their locked in a cell for 24hrs
If your a fair parent that gives reasonable guidelines like being home at 8 and don't drive past whenver then I don't think your gonna hav a problem with most kids unless they do got some problems so Id say snoop if u think somethings gonna on but don't freak out on small problems