Joanne FreemanI figure that bigger servers are slower; that they have different rules. But since you can communicate with all servers from other ones, and follow people from other servers, why change? Is it because "local" posts are only from your server? (I'll admit, I haven't looked at that category yet...newbie that I am.)
christopher little@jbf1755 I changed because the instance I was on was pretty slow, and I already had the domain name and a spare VPS around. Now I’m the only user on my server and it’s way faster.
uther 
@jbf1755 For most users, the biggest reason to change is because they don't like the moderation on the instance (too strict or too lax) or they may prefer moving from larger instance to smaller instance (or vice versa) for the feel of the community.
Another reason people consider moving instances is the Federation policy of the instance (too strict or too lax).
But in general you are right, all the servers can talk to each other (except in cases of instance Federation Silence or Suspend).
Chris Eliopoulos@jbf1755 I know my server's curator says that .social doesn't block mastdn.io who has an Italian neo-fascist group, so they "silenced" .social. So, anyone that follows me from there, I have to approve. I guess that means aligning with a server that follows your values.
MNTLe DMGD@jbf1755 what I've found is that the vast majority of those who migrate out to smaller servers are either looking for a more curated experience with a smaller community, or wanting a more open environment with less moderation. Not necessarily for extremist content, but to be able to voice an unpopular opinion. Some move because smaller servers tend to be faster and not prone to the slowdown associated with large amount of users during peak hours.
Jim Wald@jbf1755 That's what I've always thought: for focus.
A lot of people (most?) joined Mastodon Social in the beginning of the Great Migration because it was an easy and obvious choice. But other people prefer to join an instance whose community is built around their interests (including academic and technical).
I think this piece, though geared to natural scientists, describes things well:
Should I join Mastodon? A scientists’ guide to Twitter’s rival https://www.nature.com/articles/d41586-022-03668-7?utm_source=Nature+Briefing&utm_campaign=16df11fc16-briefing-wk-20221111&utm_medium=email&utm_term=0_c9dfd39373-16df11fc16-42695035
@jbf1755 Oh--forgot to add: if you use Debirdify to locate your Twitter followers on Mastodon, it provides you with a list as well as graph of which instances they are using.
BlueDot🇺🇦@jbf1755 Someone on my instance might want to move to another one if they didn't like my rules, or my responsiveness to problem reports, or the choices I've made to defederate from various right wing troll servers.
And since I'm also a newb, it hasn't come up yet.
Annabella Pomeranian@jbf1755 I’m baffled by this site. Twitter was so easy. This place is confusing.
@PomBella I didn't understand Twitter at first. This is just different. I think.
Gabriel Glickman@jbf1755 I can’t even figure out which server I’m on 😂