It's a fine line. I have found the more restrictive I get on a forum I admin on, the less the member base improves. Last thing you want to do is turn away possible members (usually). One thing to also keep in mind, there are probably more members than not that never make a single post, and yet frequent the forum 1+ times a day. I do set a minimum 1 wk time frame for outside links. I also have a setting for number of posts within a couple minute time frame.
If you make it too difficult or uninviting, folks will just stop showing up because the effort isn't worth the hassle.
Also, the more settings, restrictions, etc you put in place usually equates to more time spent by admin and mods who are usually volunteering their time. Once it becomes to much of a job, sometimes they stop showing up as well...
