Agile requirements are a product owner's best friend. Product owners who don't use agile requirements get caught up with spec'ing out every detail to deliver the right software (then cross their fingers hoping they've spec'ed out the right things).
Agile requirements, on the other hand, depend on a shared understanding of the customer that is shared between the product owner, designer, and the development team. That shared understanding and empathy for the target customer unlocks hidden bandwidth for product owners. They can focus on higher-level requirements and leave implementation details to the development team, who is fully equipped to do so – again, because of that shared understanding.
When writing a requirements document, it's helpful to use a consistent template across the team so everyone can follow along and give feedback. At Atlassian, we use Confluence to create product requirements with the product requirements blueprint.
Agile & Scrum Consultant