You don’t need more than one account. You just decide which instance you want an account on, then subscribe to all the topics you care about across multiple instances. I just think that generalist instances with thousands of local topics are unnecessary.
You don’t have to sign up on multiple sites, you just subscribe to specific channels you care about from the site you signed up for. For instance, signing up to lemmy.ml’s Politics, Lemmy.world’s Tech, and fedia.io’s Cats.
For instance, here’s a link to !startrek@startrek.website that you can interact with and subscribe to from your Lemmy.ml account: https://lemmy.ml/c/startrek@startrek.website