Shared Fates in Final Fantasy Xiv
What are Shared FATEs?
Shadowbringers introduced a variety of new features, one of which being the shared FATEs. This added a little bit of incentive for doing FATEs by providing a currency, shops, and a reputation system for those shops. The currency is called bicolor gemstones (gems for short) and is currently capped at 1000 (on launch it was 500).
You can locate your status and currency by going to the menu's Travel section and selecting shared FATE.
There are 3 ranks for each of the 6 monster zones.
The starting rank. The shop has normal quality materials available for purchase.
Unlocked by earning a gold rating for 6 FATEs in the zone. The shop now has the riding map for that zone and the High Quality versions of the materials.
Unlocked by earning a gold rating for 60 FATEs in the zone. The shop now has extra rewards such as orchestrion rolls, bardings, minions, furniture, and cards.
Completing All the Zones
If you rank all zones to max, this will grant you an achievement with a title reward of "The Invisible Hand".
In addition, you will unlock 2 more shops: one in the Crystarium, one in Eulmore.
Both of these shops will have all of the normal quality and high quality materials from the regional shops (but not the riding maps and extra rewards from the other zones). They will each have extra rewards to purchase such as the Dancer barding in Eulmore, and of course new orchestrion rolls.
There are also special achievement FATEs in each zone. Most of them give the same rewards as a regular FATE, but there are two of them that are extra special.
The achievement FATEs in Kholusia and the Tempest will grant 72 gems if it succeeds and 60 if it fails (assuming full credit). As such, even if the FATE will time out, it is still worth doing heals and damage to keep earning credit for the gold rating.
Farming Bicolor Gemstones Efficiently in FFXIV
Tempest is easily the best zone to farm in, but let's go over why by ranking them from worst to best.
Because of the way the map is laid out, flying between east and west can be annoying as some parts are cut off because of the height limit. This makes Rak'tika a very frustrating experience. (That being said, Rak'tika does have a small benefit in that if the Tojil fate chain spawns, they're very fast.)
This zone isn't too bad. There is a split but it's even at least. However there's no real other benefit to the zone. It's not good or bad; it just is.
Kholusia's map split is quite awful because it's requires going up and fates spawn on both sides in such a way that sticking to only one side would lead to a lot of downtime. The one good thing about Kholusia, and the only reason why it's ranked above Amh Araeng, is that if the special fate isn't on cooldown, you could spawn it for some awesome gem rewards. If you don't know if the rare fate is available, and don't want to take the chance, then it ranks dead last - even lower than Rak'tika because going up/down the split takes longer than dealing with Rak'tika's collisions.
Il Mheg's split may seem like it would be bad for its map, but there are very few fates on the east side and the west side fates spawn fairly quickly. As such, it can be quite fast to just fate farm on the east side, which has two fast boss fates.
Lakeland's benefit is that it's the first zone with no flying required and as such it's accessible if you wanted to gem farm with a fresh 70 (whether yourself on an alt or a friend). It has a very easy map.
Tempest has a map split but most of the fates aren't there (only 1 is, aside from the special fate) and thus staying on the north and mid (which is a slight split) side is very possible. It has the additional chance of spawning a special fate if it's not on cooldown.
Most importantly you will not be synced down at 80. Unlike the other 5 zones where you'll get synced to a level if you're higher, and thus have a forced item sync to the highest ilvl of that level, in the Tempest as an 80 you keep your item level while doing fates that are tuned for level 79 players. Thus every item level increase at endgame makes farming here solo or duo more efficient over time.