One thing that might not be obvious is that the All feed is different too, as it only shows posts from communities someone on the instance has subscribed to. But since there are ways to search communities across instances, it isn’t really a big deal. Unless you’re on an instance of one or two people maybe.

Federation and moderation are probably where the instance matters most. Also, the matter of who runs the instance is kind of important considering stability and longevity of the instance. (mine for example will probably be gone within a month once I break something)