To slightly disagree with the last 2 comments, materia can generally be disregarded for the adventuring classes. You will need 2 grade-3 materia as part of the relic quest after you get to 50 but that is it.

For the crafting and gathering classes materia is essential .. but only once you get to level 50 and have all the best gear available at the time. In order to gather from 2* nodes you need the best ilvl55 gathering gear with lots of materia melded to it.