*is not familiar with this forum and therefore doesn't know if real or joke topic* Rare Candy raises one Pokemon's level by 1 and then the item dissapears.
If you are playing just the main game, there is no real penalty to this, but if you are playing competitve vs. other human players with a level cap, it ends up reducing your maximum stats. If you plan to go to Level100, you can "Box Trick" the "lost" stats back later. --- Klonoa sigs on hold for the greater good until Earthbound is on VC or Nintendo Power's poll closes. Email your top 5 VC picks to firstname.lastname@example.org
btw seeing as how some items never disappear this question actually has some worth.
Not to mention the answer hasn't been agreed on. Sam claims you can have just one rare candy and use it an infinite amount of times.
Who knows what answer the kid was looking for? He probably thought after about 10 levels the poke stops trying to evolve. Either way look at how a routine help topic affected your life and made you look like a huge ass.