The ni.hil.ist instance runs the hometown mod of mastodon, which enables defederated, local-only posts to allow greater user privacy and control. So if you follow someone here, you might not see all their posts unless you have a local account.
@deserter Upon further thought, no, neither of those options do the same thing as local-only. https://docs.joinmastodon.org/user/posting/ gives a run down of the stock options. What this does is limit visibility only to users of this instance, rather than your followers or the wider feed etc etc.