It's called fusion. It's something Gems can do with each other. When two Gems are too weak on their own to do something, they can fuse to become stronger, and bigger. But since Gems who don't need to be fighting shouldn't be doing fighting to begin with, and the Gems who are meant to be fighting are strong enough to do anything they should need to, there's no purpose for it.
SORRY IM CYCLING THROUGH THE SAME LIKE 3 ICONS because im too lazy to upgrade yet
[ Well, there's no harm in talking about it. ]
It's called fusion. It's something Gems can do with each other. When two Gems are too weak on their own to do something, they can fuse to become stronger, and bigger. But since Gems who don't need to be fighting shouldn't be doing fighting to begin with, and the Gems who are meant to be fighting are strong enough to do anything they should need to, there's no purpose for it.