Followers are neither vitally important, nor something you can just automatically expect.
But they still matter.
I've often used this and similar microblogging just as a kind of notepad, writing down ideas and info/evidence for something I'm working on, meaning it does have some *small* value even when no-one reads it.
But even that rather unexciting way of using these platforms benefits tremendously from interaction with an audience, even a small one.
Enhancing discovery of accounts you might enjoy interacting with is pretty obviously... good?