Board Thread:Questions and Answers/@comment-76.111.238.35-20150614074644/@comment-3547897-20150614074946

Spheres are what'll make you have an easier time during the game. Some spheres are great to use (Legwand, Medulla, etc.) while others are just there (Bravest Blade).

As to where you'll find them, they'll eventually come. Finishing Trials and the Grand Gaia Chronicles will reward you very useful spheres.