I know this is hell late, but it's Kid's power container atau something...
Like in Naruto. Rock Lee has those weights on and he's fast. When he takes them off, he's REALLY fast.
This works for Kid, too. When his lines aren't connected and "aren't symmetrical", his true power is being held back. But when they're connected, he's all "bitch pls, imma symmetrical shinigami. over 9000 mothafucka" and he has his incredible powers.
Now, please enjoy this picture of "full shinigami" Kid.