The problem with this kind of rule in a campaign is not only that spam threads might be created every hour, you might also see an increase of number of threads with redundant topics. Topic that are already discussed a few months ago or perhaps years and the op will just say, sorry I was not able to catch that. Its the same with posts that requires them to post specially in the first 3 pages.They will post because they want to be paid and not to share anything that is worth sharing to the community.