Instances are like their own self-hosted Reddits with communities being the sub-reddits. We have (had?) r/python, r/rust, r/golang along with r/programming; we can do the same here with topic-focused instance (like this one). I can imagine there being instances like lemmygo.org, lemmypy.org etc if the Reddit exodus continues.
You don't need multiple accounts to access communities (sub-reddits) from other instances (reddit). A single account on any instance allows you to access communities from any other instance. The UX/UI is a bit wonky, but it works.
As @erlend_sh pointed out, micro-communities like cli, wasm, networking etc can potentially become big enough and/or have specifics that are more suitable to exist on a topic-based instance.
Personally, I don't have any preference. I will simply subscribe to the community which is the most active on whichever instance.