Does it matter? Yes, it does. Thousands of definition and uses of the terms; purpose, vision, mission, values, etc. are used by various organisations and people.
As soon as you discover mismatches e.g. between the values of an organisations and the values of individuals from any stakeholder groups; a misalignment between the declaration of the mission and the actual daily activities and the experiences with the the products or services, etc, you might start looking for a consistent explanation of these terms.
Here is our way of explaining it. Find out the details here in a prezi.