Before every tier theres a crafted set that is the Bis for progging the fight, you want this crafted at high quality and pentamelded. This is where you make the big money on crafters, especially at the start of a new expansion.
Crafters also need their own pentamelded gear, which in-turn can lead to more gil.
And of course, potions and raidfood are needed as well.

Crafting can definately land you big money in this game but its kinda dependent on where we are in the update cycle. Ususally at the begining of new exapnsions or raid tiers is when you can make big money. Hell I made my first 30m gil just selling crafter's materia at the start of Pandaemonium