Focusing on relevance when creating new notes helps avoid confirmation bias. In the Circular process of writing, ideas are developed bottom-up instead of decising on a hypothesis or a topic first. There's no topic/hypothesis yet when you write new notes – there's nothing yet to confirm! And therefore, the main criterion should be relevance.
And adding diverse notes—including dis-confirming, contradicting ideas—enriches your zettelkasten. It enables to create more connections in it. More ideas can emerge from it.
The resulting writing is also more interesting because it comes from a discussion of pros and cons rather than piling up confirming ideas.