I mean, for instance, there are multiple, idk, Technology oriented communities. I just subscribe to all of them, or at least the ones with a significant amount of users. In time, a "main" one will probably emerge among them.
Cats don't give a fuck where you think they "should" poop, they will go in the most suitable place they can find, and it's your job to make sure their litter box is the most suitable place. If they go somewhere else it's because you failed at your job.
And if cats = users and litterboxes = websites, Reddit would still be completely full of shit.
Later down the line? Yeah, definitely. Your home instance determines the following things:
Who your admin is. Your admin has a lot of control over the instance. If spez started an instance, I'm fairly confident the entire fediverse community would avoid it.
What the rules are. How strict is the moderation? What are the standards you're supposed to hold yourself to? Some are lax, some are more stringent.
How popular is your instance? In general, less popular = better. You're gonna see the big recommended instances buckle and error over the course of the day. I'm kinda guilty of this, being on sh.itjust.works, but if it gets too bad I'll probably make myself a temporary account on another instance. I really like how @theDude@sh.itjust.works is organizing stuff and I want the community to succeed. If that means reducing the load for a bit, I'll happily do it.
Sometimes if the instance creator has certain restrictions (rare). Also it affects what posts show up in the "Local" tab (posts from communities that are hosted on that instance). In the "Communities" tab it will show communities that people on your instance are subscribed to. If your instance goes down, you will lose your account I think.
Most of the time your home instance does not matter