During spam attacks we, as a community, are happily flagging posts as spam. On most sites spam posts are not long-lived. However on sites with low traffic it can take a while before spam posts reach their 6 required flags, more often than not by community members that call out for help in chatrooms.
The number of flags a day (10 but raising with your rep) per site can be fully consumed by just spam flags and after that you're out of the game.
I rather see that the spam-flags raised are not counted towards the daily-site-limit if, and only if, the post is flagged by 5 other community members as spam. The spam-flag limit should be a network-wide-limit, so you could use flags from other sites associated with your account for spam flags, and topped at the maxiumnumber of flags per day, based on your reputation with a maxium of 100 flags.
I've seen and read:
Better tools to handle spam on low traffic sites is without an answer but a lengthy comment discussion.