Some advantages of the points system (according to my personal experience):
1. Because you need to points to post, you are forced to review. So, the points system encourages reviewing. Of course, you may prefer to review the work of those authors who have reciprocated you, or with whom you regularly reciprocate. The latter can be done without the points system, so somebody may assume points are useless. Please, bear with me.
2. According to SOL's secret formula, you receive less points for reviewing than the ones you need to post. E.g., if posting 1000 words costs 5 points, you only receive 1.5 for reviewing a work 1000 words long. The proportion is not exact because only SOL has access to his top secret formula, but you've got the idea. My personal belief is that when you review you get one fifth of the points you need to publish, give or take. It may seem unfair, but the result is positive because, for every chapter you publish, you need to review from three to four chapters/short stories/poems. I.e., the points system encourages wider reviewing.
If the system pay the points 1 to 1, you'd only need to review 1 chapter more or less your chapter's length to to publish yours. If there were no points, you'd only review one chapter of some fellow writer and wait until she would review one of your chapters in exchange. Any of these two methods encourage less reviewing.
3. If you don't have enough points to publish your next chapter, and if you've already reviewed all the work/the work you like of the authors you regularly reciprocate with, the points systems forces you to review anybody else's work, whether they reciprocate or not. If they don't reciprocate, you may never review their work again, but not necessarily. If you need points, you may continue reviewing only because you need the points, or because you've just bumped into a story you like. You might have never started this sort of "fishing"--looking for random stories to review--if the point system do not exist (Why for? Unless you specifically want to look for something new. Without points you can publish, then review your friends' work, and sit until one of them reciprocates). Once again, the points system encourages reviewing.
I'm sure people will say that there are many authors publishing without points who are receiving reviews. I'm also sure that there are authors in the points system receiving no reviews. It means that neither system--points or no points--guarantees anything. However, it's my belief that the points system encourages reviews because of the above reasons.
Kiss,
Gacela