So, it’s a subtle detail and may not matter for many folks, but your instance choice affects your remote communities via the All feed, as the people there choose which of those to subscribe to & presumably discuss the posts there & post there themselves. It’s something that isn’t as clear on Lemmy yet as many instances are more general subject than focused at the moment and communities are still in the works, but it’s really clear on smaller Mastodon instances.

Easy example would be like a tech or programming instance that strictly limits the creation of their local communities, e.g. programming.dev. Off the bat you know a lot of discussion there’s to do with programming, and in turn there’s a decent chance that many of the communities people follow through there may also be programming or tech related, so the all feed may have a largely tech/programming focus to it.

As time goes on, you may see more focused instances with stricter sign-ups specifically to ensure their all feed relates more to their community’s focus, but honestly probably not too many as people enjoy flexibility in their posting.