It negatively affects crowdsourcing. You have people all over the internet linking to a specific forum. Any of a thousand thousand people might stumble on a particular thread in this forum. A person with crucial insight or knowledge on the issue at hand might look for the reply button, in eager anticipation of his stunning ability to dazzle people in this particular area of expertise.

Bewildered by the lack of reply-button he might think that signing up will grant posting privileges. Once this does not pan out he will eventually either leave or end up finding the newbie section and all these procedures for getting in. Upon seeing all of this hokey stuff, the person will then make a second decision, to put up with it and either keep posting (four hours five posts and all that) or stand at the mercy of an admin being willing to post his comment (which, in contemplating spending 30 minutes writing a post, might be too much of a risk).

No, more likely - and especially if this is a busy person with other, more important things to do (unlike me, etc.), the person will simply leave the site and never bother with it - until the cycle repeats the next time his knowledge and insight is occasioned by a link to this forum.