it depends on which game you scan em.
for super smash ur amiibo , becomes the cpu of the character you got exemple megaman you'd unlock a megaman cpu , which you can level up to level 50. (compared to the level 9 you originally get) and then he picks onto your fighting style , i.e if you keep spamming tornado , your amiibo will also ust spam tornado.
for mario kart 8 you unlock some crappy customs for the amiibo
for hyrule warrior : link unlocks a weapon , zelda unlocks a weapon also toon link and the others just unlock random stuff.
for code name steam : ike , marth , robin , lucina and whatever other fire emblem they're may be. it will unlock it as a character.