Yes, while AP is not required to play the game, it mainly gives the advantage of convenience, vanity, and with specific items, stat bonuses.
You can take a look at the Web Item Mall
here or by pressing "i" in-game to see what's available directly from that item mall. Items that offer EXP and CP bonuses, dyes for costumes and class outfits, scrolls and safety stones for upgrading equipment, bags for extra space, etc.
You may also be interested in the various AP Promotions
that take place, allowing you to receive bonus items for buying certain things, or during certain times, such as in the Tiered events.
Regarding money-making in the game, yes, many players make gold quickly by selling AP items that are in high demand, such as Eden Crystals, Safety Stones, Auric/Iris Jewels, and bags.
Let us know if you have more questions!