http://blog.secondlife.com/2008/05/05/changes-to-groups-new-rules-on-group-notices/

With the new feature on notices scrolling off after 200 notices sent per day, it becomes highly necessary for a group owner to be able to limit the number of notices an individual can send in a group to avoid abuse of the group notices feature.

It already happens in some large active groups that the notices feature gets abused. Even though groups often have rules on limits on how many notices can be sent by a person in announcement groups, we are at the mercy of the person sending the notice that they will follow the rules. It's already a situation that people lose their posting priveledges but the main problem with this is that it happens after the fact, and in a worst case scenario, the notices could be abused to actually grief the group to scroll its archive, so that older posts disappear and the performance of the group grinds to a halt, forcing users to quit the group to stop receiving the notices. Much the same way that griefers scroll chat. This was not so much a problem before as notices expired in a set period of time, but now that the notices archive can be actively scrolled by users I fear abuse, as this is a common sort of abuse in forums and chat for quite many years.