99% of all drafted players never think about free agency but would be glad to play a single day in mlb.
But if you are such a blue chip prospect that you think about free agency when you are drafted you need to make sure you get drafted as young as possible and then move through the minors as fast as possible. I think harper had that in mind when he did his thing. Harper got drafted at 17 and made the majors at 19 and his young free agency age is a significant advantage. Compared to that college players are usually already 30 at free agency which is a disadvantage because teams don't like to sign past age 35 anymore.
The anti harper example would be peter alonso. He is already like 24.5 years old when he makes the majors and almost 32 at free agency. As a corner guy this will hurt his stock and probably relegate him to one or two year deals.
But as I said this is a longshot for most, only top5 overall picks can think like that, most others won't make it to year 6 in mlb if they make it to mlb at all.