[quote user="Vector"]I'm a global moderator at a fairly popular active forum (Currently sitting on 3,400 members and about cumulative 215,250 posts).
In terms of administration, registration can make the job easier to keep no-gooders out.
You get people who, if they aren't accepted by the general community because they are total tossers, try to post in other people's names, and generally post shit all over the forums. You get spambots posting page-long ads for garbage you'll never want. We've even had a "stalker" of sorts. All that kinda stuff.
Requiring registrations and manually approving new ones (which only takes a a minute each day) is a fairly sound way of avoiding all of that shit. And then, if something does go up the creek you can just delete that person's account and never have to worry about them again - you know what e-mail address they might use to try and register a different account, you know their IP range (assuming they're not using AOL), and if they manage to slip through, you just delete them again.
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Tripcodes and/or secure tripcodes, simply hashes of something you enter on the page, get rid of people impersonating other people (The secure ones are salted with different salts per board).
For spambots, there's simple spamtraps (That will easily keep general-purpose spambots out) and captchas, if necesary.
How would registration keep no-gooders out anyways? 15-Year old bored trolls with nothing else to do than to annoy people in online forums have enough time to register anyways, multiple accounts if neccesary, via TOR or loads of proxys. People who might actually have something to contribute, on the other hand, might decide to not post because they can't be bothered to go throuh a registration procedure, which might even take hours to be finalized.
This type of board works pretty well for 2channel, which is community-moderated and gets ~2.3 million posts per day - http://stats.2ch.net/suzume.cgi?yes .
(Better article about 2chlike boards: http://wakaba.c3.cx/shii/shiichan )