Gregory's Server@darius it largely depends on your goals with Mastodon. I've heard many people wanting to migrate here from Twitter due to the...new CEO. It's a huge opportunity to popularize the Fediverse and turning off open registration turns them away. For me, this was the only remotely relevant instance where I could register and that's not good. Then again, every community has the right and interest to defend itself.
@smicur yes but consider: letting 5000 people sign up and then having your server crash and burn either technically or socially means you have 5000 people who come away from that thinking federation doesn't really work