You don't have to invite people to your pool if you don't want to.  It's entirely up to you.

The way I understand it is that the largest pools will receive the best interest rates, but also have higher risk for defaults.

So if you invite someone to your pool, you are in a sense "cosigning" on their loan.  If you email him, he can send you a list of the pools that are currently running.  I have had a few correspondents back and forth between him.

Ran into him on tor website.  One I would rather not mention.