In FFXIV, one of the new features of Heavensward was the Undersized party option. Frankly, I think the name should be Unsynced rather than Undersized as it fits a little better. Undersized implies that you must have less party members than the standard. So for standard 4-man dungeons, this means 3 members and under, and for 8-man dungeons, this means 7 members and under.
To activate the undersized party options, bring up the Duty Finder. There is a cog wheel near the Language options located at the top of the menu. This cog is the Duty Finder Settings. Open that up and you will see two options. Undersized Party and Minimum IL.
Not all duties can be selected when using the Undersized Party option. All of A Realm Reborn’s dungeons, Trials, and Coil can be done using this option. The Crystal Tower saga, guildhests, duty roulette and Heavensward dungeons and trials cannot be used in conjunction with the undersized party option.
Using this option will not net you any experience points or loot that drops from enemies. However, treasure coffers still appear – this includes the ones scattered in the dungeon as well as when a boss has been defeated. Yes, this means you can go into the extreme primals of A Realm Reborn as an undersized party and the weapons/accessories and ponies will drop.
Zodiac items from dungeons can also drop using this option too. Just remember that these drop when you exit the dungeon, not upon the bosses defeat. Undersized will put you into the duty as the level you are. No being synced down if you happen to be a higher level than the duty usually allows. This means you can go into, say Sastasha, when you’re level 60 and stay being 60 rather than being synced to level 18.
While you can deal more damage and take more hits, some mechanics will still kill you. So you’re not too invincible. And some mechanics of the primals will still wipe the party if you’re not careful. Sometimes, dealing too much damage can be a bad thing.