Pocket Legends is setup so that people can't simply "buy" there way through and simply get some platinum and buy all the good pinks. Instead, it's setup were the very best and rarest items can only be gotten from monster drops, but also have a item shop that has some "special items" for those people that buy platinum and want something that looks cool, but is not neccasarly the best item stat wise for your level.

So, you will need to buy platinum to purchase the various dungeons were the monsters are located that drop these various rares. But the only items you might want to purchase with platinum are some of the cool Vanity items such as a Holiday Hat or Blueberry Beret, which give no stat bonuses but have a very nice look