3rd Retainer by Default, please?

[Nyalia]

I cant even fathom how you people can use so much space.

Most of it is glamour, or leveling equips for new jobs when they're released. Consider the pre-50 unique dungeon gear (some untradeable, some not): there are 3-4 sets at each tier (tank, physical DPS, healer/caster, and then sometimes DRG gets their own set). There's a tier at level 15 (acolyte, foestriker, plundered [extra versions of plundered for some slots]), level 20 ([not full sets]), level 24 ([not full sets]), level 32 (battlemage, infantry, cavalry), level 38 ([not full sets]), and level 44 (buccaneer, templar, harlequin, and sentinel). There are also dungeon sets at i55, i60, i70, i80, i100, and the higher you get, the more these are specific to a smaller set of classes so you get more of them. Then there's the philo, myth, soldiery, and poetics sets, the LotA, ST, and WoD sets, the First, Second, and Final Coil sets, and then all the highly expensive glamour items.

If you're someone who likes to leave options open for glamour, you have to store something like 3 types * 5 slots * 21 tiers = 315 items. And that's assuming there's only three sets per tier (at the higher tiers, there are six (fending, healing, casting, maiming, striking, aiming), at the highest, there are seven (fending, healing, casting, maiming, striking, ranging, scouting), and for Myth, there are ten). This ignores the crafted sets, even though the high end sets (i70, i90, i110) are not ones where you'd just make an item for glamour and then throw it away because you can get a new one due to their priciness. Oh, and I didn't include the PvP gear where, for the i100 and i110 items, there are 10 sets of each (plus some of the i90 gear has a pretty unique look, iirc). It's also assuming you only care about the five primary glamour slots - it doubles if you add in accessories/belts, and skyrockets if you include weapons.

To completionists who like to have access to one of everything (at least for something like glamour), it's not unreasonable to try to get the whole set for most of these, especially the unique endgame sets like the ST and Second Coil sets. Because of class restrictions on the glamour system, it's often not enough to have one item with a given look - even if two classes have gear that looks the same except for a recolor, due to the class restrictions, you need to keep both.

So, ignoring crafting mats, atma, dyes, materia, demimateria, gardening items, food, choco feed, unused furniture, potions, unarmoireable seasonal/achievement items, fireworks, maps, and wedding invitations, it's definitely possible to run out of your 450 inventory slots (and 300 armory chest slots, which need to include stuff like crafting/gathering gear and your actively used gear for each class) just by keeping items for glamour.