It's certainly not a one size fits all. One huge problem is that advisors, like recruiters, and scouts need to throw a lot of stuff on the wall to some to stick. The draft process - which begins early enough so scouts can build a data base for real use in the kids draft year - for adviso/kid relationships is a lot like the recruiting process in that the advisor does hundreds, thousands of kids and the family does (usually) one draft. Therefore, the advisor knows the magic words to warm a family's heart (something along the lines of "he's got some tools"), knows that a HS junior (or even below) and his family are on the other side of the learning curve, and can take advantage of that mismatch. Just like the RC can and often does.
If a family uses an advisor (and I'll assume no future NCAA issues - even though I have seen a bunch of half year sit outs by those who fell afoul of the advisor rules) it becomes convenient to use the advisor as THE source of information; and I think that's wrong. The family needs to muddle though the learning curve - it's only then that the family can really immerse themselves in the details which will be needed to decide which option is best for your kid.
Keep in mind the advisors financial incentives: no money until proball. Alway, always, always understand the incentives of these people. A family, and their own coaches, can determine if a kid in 11 (or lower) has a path to proball out of HS; no need for an advisor to tell you that. In this day and age, the Internet is a treasure trove of info needed to determine (a) if kid is good enough to (b) make the decision to place proball before college. Then the question becomes: at what price? I've seen HS guys sign for 35k and I've seen college juniors not sign for 150K; so the decision is personal. This is a decision which must be made by the kid and the family - an advisor who is giving out more than sources the family should read directly at the early stage we're writing about here, is, IMO, intruding. What a 11th grader (or younger) should be worrying about is improving his baseball skills, grades, scores, and keeping out of trouble. The advisor brings way too much too soon. This is the family's joint job - and for kids that age, the family has plenty of time to learn the process.
But, so long as you realize that the decision, the input, your son's future, all of it, is on the family and no part of it can be laid off on an advisor.
Please remember, I'm addressing my own personal opinion on advisors for pre-draft year kids; not draft year kids where an advisor can help maintain sanity when everyone in the house is feeling - shall we say - somewhat stressed.