@Eleefunt Whoever runs the server technically has access to all of your data and can do anything they want with it. So, there's a bit of trust involved in who you choose for that responsibility. Other than that, it comes down to who you will see in your "local" timeline, which will show you people on your server. Popular posts on your server will also show in the Home section. Different servers draw different crowds and communities.

@thomasreggi @Eleefunt I think of them as communities. Each community is a bit different but just because you are in 1 neighborhood does not mean you cannot interact with others. The instances can be configured to be aware of other instances. I think the big thing in social media is for the different communities to be in control. In the literal sense they are the servers that you post your updates to and control latency and privacy.