I figure that anyone could figure out how respectable someone is just by viewing a post or two that they've made. If someone's a good person, it usually shows through in their posts

One shouldn't need any sort or reputation system just to tell if someone's respectable. The tiers can also almost end up being a measurement of how active someone is. If you're inactive, you won't be getting any tiers. But if you're active, you likely will be. Of course, there is more to it than that, but that -is- a major factor.
Also, a tier system like we currently have can end up being partially biased or inaccurate. It doesn't necessarily show who does good things, just who is -noticed- doing good things. Or someone who's been a good person might just be forgotten when it is decided that tiers will be updated, simply because there were a lot of people who were going to be raised and one name was easy to lose. Stuff like that

I also can't really see any -helpful- purpose they can serve, but I can think of a few bad things they could lead to. Like people thinking that the admin is unfair or mean or something or has a grudge against them, or people getting jealous. Even if it never leads to open conflict, there could be a few hidden dislikes, simply because someone has a higher tier than them. Or the other way around. People looking down on others because they have a -lower- tier than them XD
... Pretty much, I just don't see any reason why they really -should- be there. It seems like things might be -easier- without them