[@Double] Well, it can be 1.5-2 times its normal size throughtout its evolutionary line. Budew would be 1'04" instead; that's practically the size of a Pikachu or Meowth. Certain moves would be affected such as the amount of water released via Water Sport and pollen with Stun Spore. The same would apply when it evolves and learn new moves. A Roserade is 2'11" but as a giant, it reach heights of 5'10" You don't need to make it a giant if you don't want to though. Its just an option.