Sometimes it's nice to be alone in a crowd without needing to interact with anyone. You can be among people but still doing your own thing. Like playing an MMO SP, or at least I assume, as I've never done such a thing. That being said I'm not of the "no entry" mindset, more just "I want to build a few things first", create an aesthetic, and then connect/open it up to the rest of the server. That way you can also control other user's interaction with what you've built. Rather than see it half built, they see it when it's completed. Maybe they also only see it via a portal for example, so they approach it from a certain preferred direction. Or you build something in the middle of no where, and months later someone exploring comes across it and is able to check it out with some interest.
So it's not about, limiting interaction. But rather having the power to determine the level and quality of interaction.