In My minecraft server that I run I have several command block clocks that run the server side mini games. The commandBlockOutput gamerule stops all those commands from spamming the chat but it still showes the output in the server console and the log files. That makes it so that I can't read the chat from either the console or the server logs and also keeps me from seeing who has been on.
Confirmed for 1.8.7, and possibly all recent versions down.
It's annoying...