Commitments with a resounding and well-communicated 'why' have the best chance of getting done well. That 'why' should not be limited to the '...so I can' element of a story headline.  A business value statement allows you to more clearly articulate why the business should invest in this story, feature or outcome NEXT.  It also allows various stakeholders (business and technical) to describe rationale for prioritizing this item that may not be obvious to the product owner - technical dependencies, regulatory or compliance demands, etc.