By blocking the messages that you consider not useful you will avoid them being sent thus avoiding some network traffic.
I made this having in mind blocking "Press the BUY key to purchase items" that is sent to clients every round and "You spotted an enemy" or "You killed an enemy. Kill all the enemies to win the round" that i find annoying, in my server.
cvars (valued as 1, means "to be blocked") (changes to them only affect after mapchange/restart)