As far as I'm concerned, there is only one legitimate use of the blocklist, and that's if someone is genuinely harassing you in chat with abusive language. When it comes to gameplay reasons, I think it's being exploited. And like I said, River, nobody using it like that is going to be spending much time in Open anyhow, so no loss.
I use it on anyone who is just out to spoil the game like station rammers, and dirty cheats. Usually both.
I also do open about 80% of the time, or I'd not bother with blocking at all.