For individuals, it's primarily access to crossbreeding for seeds that yield items that can only be obtained through gardening (other than the rare occasions those items show up in the quick venture loot tables). The garden minions (Allagan Melon, Mandragora Gang), things like Royal Fern and Blood Pepper for crafted minions, Jute and Broombush for housing items, and various other materials are gardening exclusives. Thavnairian Onions are primarily from gardening (players can get 2 from different HW quests). The player can always buy seeds on the marketboard from those that produced them through gardening.

For FC, it's access to the workshop in addition to gardening. Airships and submersibles have exclusive items on their loot table that can be sold to raise gil for FC needs so they aren't dependent on member donations.

Depending on what a player's personal goals are, those things might be seen as game play advantages. Someone focused solely on combat and power progression wouldn't but those into other parts of the game might.

Quote Originally Posted by ScottDoom View Post
Something else not mentioned is that you can stable and train your chocobo. I might be wrong, but I'm pretty sure it's required to go from a rank 10 chocobo to a rank 20.
Don't need access to a stable to do that. The Thavnairian Onions can also be fed to the chocobo while they are summoned in the zones.

A stable can make it faster for your chocobo to gain ranks since it can be trained by you and by others with access to the same stable when you don't have it summoned. Purchasing an apartment includes access to the building's stable so a house isn't strictly necessary.