Really it doesn't matter if it doesn't effect you. I use Jerboa and I'm sure most other apps work the same, you can switch between logins within the app. So if you want to join another instance, say dbzer0, which focuses around Piracy and Anarchy, you create a login from their page then sign in in your app. Switching between accounts is fluid and then if an instance you use does something to piss you off, you can slowly stop using it.

I like to think of it like a playground. We want everything spread out a bit and not all on one instance. So if the owners of that instance start to do things users don't like, you can just replace the softball field,, and keep the slides, swings, soccer fields, walking track etc. Each one of those I would be considering your main subs you are interested in. So if someone ties ads or starts being foul on that softball field, we walk away from the pitch, and onto another softball field and you keep your logins if you weren't based on that softball field. Everything else stays good. (We just start the softball field on another instance)

Edit: Note, the content you see between instances will mostly all be the same unless they have de-federated from another instance for whatever reasons. Some may de-federate from things that have NSFW content for instance, Piracy laws, etc. It's always the instance holders choice, because at the end of the day it's their hardware that is hosting whatever it was they didn't want on it.

Edit 2: more information I remembered. Some instances support things like upvotes and downvotes. Some only allow upvotes, some neither. This is all tied to what they believe may be healthier for discussion... I believe some instances may have things about infinite scrolling as well. But app settings may include those as well. I look at it as everyone trying to find their most comfortable way they find healthy to consume content.