It is my understanding that it was created as a containment board, but it's popularity and relative power has soured me on the whole site.
Here's the problem: /pol/ gets so much traffic that I can't imagine that its visitors do not cover a fairly broad subset of 4chan's entire user base. This means that if I contribute to any of the other boards I am contributing in some way to the intellectual capital pool drawn upon by the sorts of people who hang out in /pol/.
No thanks.
I'm not the only person who feels this way. I've heard others say this kind of thing too. There's a lot of people who once visited the site who no longer do so. Boards like /pol/ seem to be killing 4chan as anything other than a more Internet-cool satellite of Stormfront.
I don't think there actually are, in practice.
How do you have any sort of "containment" on an anonymous forum? There's nothing at all stopping /b/ and /pol/ from stepping into any other board and either playing along or not. The only containment there is a state of mind.