There was another thread on this about a year ago, which may be worth looking for.
In short, unless there is a legitimately serious reason, I would avoid it absolutely. By serious, I mean something that is worth potentially ruining, or at least seriously damaging, a relationship with your child over and also is worth impacting their ability to trust others in the future. Snooping through your child’s stuff, particularly when they get older, is a fantastic way to destroy trust. Unfortunately, this damage of trust is not limited to the relationship between the parent and child. It will extend into other aspects of their lives. After all, if they cannot trust mom and dad to respect their privacy, who can they trust? This can also have the side effect of teaching the child that they need to hide things from their parents, and others, and cause parents to miss other things which could be of legitimate importance down the road.
This happened to me as a teenager, more than once, and even continued into my adulthood, and not for serious reasons either (my mother was concerned about what girl I was dating). This took the shape of her looking into my personal things (notes, journal, etc.) but also in the form of sharing things with other people about my personal life. To date, I am guarded about what I say regarding my personal life, job, faith, etc. with my family and friends, and pretty much anyone. In terms of respecting my privacy, I trust my wife, and that is about it.
So, bottom line? It is not a step to be taken lightly and parents need to think beyond the particular situation they are in and decide what kind of relationship they want with their kids, and what level of guidance they will be in a position to provide, not only when their kids are in their youth but when they are in their 20’s, 30’s, etc. Do you want to be sought out for guidance when your child is thinking about marrying, having kids, deciding things about their faith, buying a house, etc? If so, you had better be absolutely sure that whatever piece of information you are considering looking for right now in the moment, is something you need to know, and not just something that you want to know.