FFXIAH Linkshell Ni

A light party will consist of a minimum of 4 players. You can have a 5-man light party, but when you reach 8 players, it becomes a full party. You can have 3 of these full parties at max, for an Alliance of 24 people.

Once a light party is formed, you will gain access to the Limit Break system, which appears above the party name plates. This normally consists of a single bar. When it is full, you can perform a limit break, which will do different things depending on which role the party member can hit it is. Each player gets a separate access to this, but once used it is used for the entire party, and must be built up again. On a boss monster, this bar is doubled, so you can perform up to two small limit breaks, or one medium limit break, which is individually more powerful than a small limit break, or two smaller ones combined. If you are on a much larger boss, such as a raid boss of one of the NM FATE bosses, you can get a third limit break bar, and this is the most powerful of the three, and for healers has an additional effect.

A full party can better crank the LB gauge up.

A party composition increases in complexity from 1 tank, 1 heal, and 2 dps to what may be useful as 2 tanks, 2 heals, 1 support, 3 DPS. The support role can be married into one of the healers for additional damage, or as in the case of Bard, as one of the DPS. Alliance composition is speculative and weak, and will likely massively depend on the encounter, but it is unlikely there will be content requring more than 3 tanks ever, but plenty of content requiring more healers. Yoshida suggests that parties will function best when the two healers they bring for a full party are White Mage and Scholar, as they have complementary but non-overlapping skills (WHM may be about single target healing, while SCH is about damage shields and heal over time effects, or HoTs), and so it is likely that having a full diverse range of classes in a 4 man party would consist of one of each:

tanks (TPS)
1 Paladin
1 Warrior
heals (HPS)
1 White Mage
1 Scholar
support (?)
1 Bard
damage
*you have two melee and 2 caster classes to choose from, but only three slots; selection is likely based on needs, but also availability and preference of the group or players:
2 casters:
1 Black Mage
1 Summoner
2 melee:
1 Monk
1 Dragoon

Both MNK and DRG bring additional skills that can improve party damage: DRG brings a debuff that increases slashing damage on the target, which increases PLD, WAR and all other DRGs in the party's damage; and MNK brings blunt damage, which only influences other MNKs. So party comp MIGHT matter in some cases.

You can also, if you WANT to, have a party structured however you wish!

Went home for lunch specifically to knock out some silly quests.