The future state defines the outcome of the change a business analyst is creating within a company.
The more clarity the business analyst has in the future state, the more clarity he/she brings to the change.
The more clarity the business analyst has in the future state, the more complete map can be created from the current state to the future state.
It is worth noting that the future state belongs to the organization. We may think we have a clear understanding of the future state, but if it is not in alignment with what the organization wants, it is not the future state.