The first is how much you know about the draft, dealing with scouts, money, slotting, etc.
The second is where you expect to be selected. At some point the choice is made for you by the "advisors" as was the case with our son. Beyond the 10th round, there is not much incentive for them. For the first 5 rounds I think it would be critical unless you really know the breadth of issues that can be addressed even down to Fall instrux.
The third and most important, I believe, is the ability of your son to focus on baseball and perform as if the draft did not exist. This requires a singular focus because the draft year is one every player knows is critical. Whether you are a first pick or projected as a filler, if you desperately want that chance to be drafted, seeing scouts or not seeing scouts at games/practices, and dealing with the indecision/anxiety that comes with the process can be an enormous distraction. An advisor should be an enormous help to minimize the distractions and maximize the opportunity to perform for some.
One of the reasons I am amazed at my son's experience is he did get a fair amount of activity from scouts, wanted to be drafted about as badly as anything in his life, got varying responses from a draft position as high as the 10th round to might get a chance as a free agent. Never once complained, found one scout he believed in and trusted for advice and had the best year he ever had in baseball. Struggled a bit with grades
but his focus was unbelieveable. I know it is not something I could have done.