chāosòng tài shǎo, hòumiàn yǒurén bù zhīdào fāshēng le shénme; chāosòng tài duō, yòu huì zhìzào zàoyīn

抄送太少，后面有人不知道发生了什么；抄送太多，又会制造噪音。

CC'ing too few people leaves some in the dark about what happened; CC'ing too many, however, just creates noise.