Recently I observe that obvious spam often gets far more down votes than spam flags would be needed for community deleting and locking:
Should we in case of an obvious spam post leave a comment so that users who don't know about the power of spam-flags will not downvote (this will remove the post from the front page and makes it harder to spot) but spam-flag appropriately to get the spam deleted more quickly?
Here is the relevant MSO link on spam flags: